Ventricular assist device with stabilized impeller

ABSTRACT

Apparatus and methods are described including a left-ventricular assist device that includes a tube configured to traverse a subject&#39;s aortic valve, with a distal portion of the tube within the subject&#39;s left ventricle. A frame disposed within the distal portion of the tube defines cells, and a width of each of the cells within a cylindrical portion of the frame is less than 2 mm. An inner lining lines at least some of the cylindrical portion of the frame. An impeller is disposed inside the frame such that a gap between an outer edge of the impeller and the inner lining is less than 1 mm. The impeller is stabilized with respect to the frame, such that, during rotation of the impeller, the gap between the outer edge of the impeller and the inner lining is maintained and is substantially constant. Other applications are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. Ser. No. 16/750,354 toTuval, entitled “Distal tip element for a ventricular assist device,”filed Jan. 23, 2020, which claims priority from:

US Provisional Patent Application 62/796,138 to Tuval, entitled“Ventricular assist device,” filed Jan. 24, 2019;

US Provisional Patent Application 62/851,716 to Tuval, entitled“Ventricular assist device,” filed May 23, 2019;

US Provisional Patent Application 62/870,821 to Tuval, entitled“Ventricular assist device,” filed Jul. 5, 2019; and

US Provisional Patent Application 62/896,026 to Tuval, entitled“Ventricular assist device,” filed Sep. 5, 2019.

The present application is related to PCT Application No.PCT/IB2020/050515 to Tuval, filed Jan. 23, 2020, entitled “Ventricularassist device,” which claims priority from the above-referenced USProvisional applications.

All of the above-referenced applications are incorporated herein byreference.

FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to medicalapparatus. Specifically, some applications of the present inventionrelate to a ventricular assist device and methods of use thereof.

BACKGROUND

Ventricular assist devices are mechanical circulatory support devicesdesigned to assist and unload cardiac chambers in order to maintain oraugment cardiac output. They are used in patients suffering from afailing heart and in patients at risk for deterioration of cardiacfunction during percutaneous coronary interventions. Most commonly, aleft-ventricular assist device is applied to a defective heart in orderto assist left-ventricular functioning. In some cases, aright-ventricular assist device is used in order to assistright-ventricular functioning. Such assist devices are either designedto be permanently implanted or mounted on a catheter for temporaryplacement.

SUMMARY OF EMBODIMENTS

In accordance with some applications of the present invention, aventricular assist device includes an impeller disposed upon an axialshaft, with a frame disposed around the impeller. The ventricular assistdevice typically includes a tube, which traverses the subject's aorticvalve, such that a proximal end of the tube is disposed in the subject'saorta and a distal end of the tube is disposed within the subject's leftventricle. The impeller, the axial shaft and the frame are disposedwithin a distal portion of the tube inside the subject's left ventricle.Typically, the impeller is configured to pump blood from the leftventricle into the aorta by rotating. The tube typically defines one ormore blood inlet openings at the distal end of the tube, via which bloodflows into the tube from the left ventricle, during operation of theimpeller. For some applications, the proximal portion of the tubedefines one or more blood outlet openings, via which blood flows fromthe tube into the ascending aorta, during operation of the impeller.

For some applications, the ventricular assist device includes adistal-tip element configured to define a straight proximal portion thatdefines a longitudinal axis, and a curved distal portion shaped such asto curve in a first direction with respect to the longitudinal axis ofthe straight proximal portion before passing through an inflection pointand curving in a second direction with respect to the longitudinal axisof the straight proximal portion, such that the curved distal portiondefines a bulge on one side of the longitudinal axis of the straightproximal portion. Typically, the distal-tip element has a question-markshape and/or a tennis-racket shape.

For some applications, the distal-tip element is configured to separatethe blood inlet opening from a posterior wall of the subject's leftventricle when the distal-tip element is placed against the apex of thesubject's left ventricle. Typically, the distal-tip element isconfigured to separate the blood inlet opening from a septal wall of thesubject's left ventricle as the distal-tip element contacts the apex ofthe subject's left ventricle. Further typically, the distal-tip elementis configured such that, when distal-tip element is inserted into theleft ventricle such that the bulge bulges toward the septal wall, inresponse to the distal-tip element being pushed against the apex of thesubject's left ventricle, the blood inlet opening gets pushed away fromthe septal wall and toward a free wall of the subject's left ventricle.For some applications, the blood inlet opening gets pushed away from theseptal wall and toward the free wall of the subject's left ventricle bythe straight proximal portion of the distal-tip element pivoting aboutthe curved distal portion of the distal-tip element.

For some applications, a duckbill valve is disposed within a distal-most10 mm of the distal-tip element. Typically, the duckbill valve defines awide inlet and a narrow tip that defines a slit therethrough, theduckbill valve being proximally facing, such that the wide inlet faces adistal end of the distal-tip element and such that the narrow tip facesaway from the distal end of the distal-tip element. For someapplications, the ventricular assist device is configured for use with aguidewire, and the distal-tip element defines a guidewire lumen. Forsome such applications, the ventricular assist device further comprisesa guidewire guide disposed within the guidewire lumen at a location thatis proximal to the duckbill valve. The guidewire guide is typicallyshaped to define a hole therethrough, which narrows in diameter from aproximal end of the guidewire guide to a distal end of the guidewireguide, the shape of the guidewire guide being configured to guide a tipof the guidewire toward the slit at the narrow, proximal end of theduckbill valve, when the guidewire is inserted from a proximal end ofthe left-ventricular assist device. For some applications, the duckbillvalve is shaped to define a converging guide portion at its proximalend, the converging guide portion converging toward the slit, such thatthe guide portion is configured to further guide the tip of theguidewire toward the slit.

Typically, the frame that is disposed around the impeller defines aplurality of cells, and the frame is configured such that, in anon-radially-constrained configuration of the frame, the frame comprisesa generally cylindrical portion. Further typically, a width of each ofthe cells within the cylindrical portion, as measured around acircumference of the cylindrical portion, is less than 2 mm (e.g.,1.4-1.6 mm, or 1.6-1.8 mm). For some applications, an inner lining linesat least the cylindrical portion of the frame, and the impeller isdisposed inside the frame such that, in a non-radially-constrainedconfiguration of the impeller, at a location at which a span of theimpeller is at its maximum, the impeller is disposed within thecylindrical portion of the frame, such that a gap between an outer edgeof the impeller and the inner lining is less than 1 mm (e.g., less than0.4 mm). Typically, the impeller is configured to rotate such as to pumpblood from the left ventricle to the aorta, and to be stabilized withrespect to the frame, such that, during rotation of the impeller, thegap between the outer edge of the impeller and the inner lining ismaintained and is substantially constant. For some applications, theimpeller is configured to reduce a risk of hemolysis, by beingstabilized with respect to the frame, relative to if the impeller werenot stabilized with respect to the frame.

For some applications, proximal and distal radial bearings are disposed,respectively, at proximal and distal ends of the frame, and an axialshaft passes through the proximal and distal radial bearings. Typically,the impeller is stabilized with respect to the frame by the impellerbeing held in a radially-fixed position with respect to the axial shaftand the axial shaft being rigid. For some applications, the impellerincludes bushings that are disposed around the axial shaft, and at leastone of the bushings is configured to be slidable with respect to theaxial shaft. For some applications, the impeller being stabilized withrespect to the frame by a region along the axial shaft over which the atleast one bushing is configured to be slidable with respect to the axialshaft being coated, such as to substantially prevent the impeller fromvibrating, by reducing a gap between the at least one bushing and theimpeller. For example, the region may be coated in a diamond-like-carboncoating, a polytetrafluoroethylene coating, and/or a polymeric sleeve.

For some applications, the frame defines struts having a structure thatis such that, as the frame transitions from a proximal end of the frametoward a center of the frame, the struts pass through junctions, atwhich pairs of struts branch from a single strut, in a Y-shape. Thestructure of the struts of the frame is typically configured such that,in response to a distal end of the delivery catheter and the frame beingmoved into overlapping positions with respect to each other (e.g., bythe distal end of the delivery catheter being advanced over the frame,or by the frame being retracted into the distal end of the deliverycatheter), the frame is configured to assume its radially-constrainedconfiguration by becoming axially elongated, and is configured to causethe impeller to assume its radially constrained configuration bybecoming axially elongated (e.g., by the pairs of struts that branchfrom each of junctions being configured to pivot about the junction andmove closer to each other such as to close in response to a distal endof the delivery catheter and the frame being moved into overlappingpositions with respect to each other).

For some applications, a housing for an impeller of a blood pump ismanufactured by performing the following steps. An inner lining isplaced around a mandrel. A cylindrical portion of a frame is placedaround the inner lining, the cylindrical portion of the frame includingstruts that define a generally cylindrical shape. A distal portion of anelongate tube is placed around at least a portion of the frame, the tubeincluding a proximal portion that defines at least one blood outletopening. While the distal portion is disposed around at least theportion of the frame, the inner lining, the frame and the distal portionof the elongate tube are heated, via the mandrel. While heating theinner lining, the frame and the distal portion of the elongate tube,pressure is applied from outside the distal portion of the elongatetube, such as to cause the distal portion of the elongate tube toconform with a structure of the struts of the frame, and such as tocause the inner lining and the distal portion of the elongate tube tobecome coupled to the frame. For example, the pressure may be applied bymeans of a silicone tube that is placed outside the distal portion ofthe elongate tube. For some applications, the inner lining and theelongate tube include an inner lining and elongate tube that are madefrom different materials from each other, and a thermoformingtemperature of a material from which the inner lining is made is higherthan a thermoforming temperature of a material from which the elongatetube is made. For some such applications, the inner lining, the frameand the distal portion of the elongate tube are heated to a temperaturethat is above the thermoforming temperature of the material from whichthe elongate tube is made and below the thermoforming temperature of thematerial from which the inner lining is made.

For some applications, the impeller is manufactured by forming astructure having first and second bushings at proximal and distal endsof the structure, the first and second bushings being connected to oneanother by at least one elongate element. The at least one elongateelement is made to radially expand and form at least one helicalelongate element, at least partially by axially compressing thestructure. An elastomeric material is coupled to the at least onehelical elongate element, such that the at least one helical elongateelement with the elastomeric material coupled thereto defines a blade ofthe impeller. Typically, the coupling is performed such that a layer ofthe material is disposed around a radially outer edge of the at leastone helical elongate element, the layer of material forming theeffective edge of the impeller blade (i.e., the edge at which theimpeller's blood-pumping functionality substantially ceases to beeffective). Further typically, the method includes performing a step toenhance bonding of the elastomeric material to the at least one helicalelongate element in a manner that does not cause a protrusion from theeffective edge of the impeller blade. For example, sutures may be placedwithin grooves defined by the at least one helical elongate element,such that the sutures do not protrude from the radially outer edge ofthe helical elongate element, the sutures being configured to enhancebonding of the elastomeric material to the at least one helical elongateelement. Alternatively or additionally, a tightly-wound coil is placedaround the at least one helical elongate element, such that theelastomeric material forms a substantially smooth layer along a radiallyouter edge of the coil, the coil being configured to enhance bonding ofthe elastomeric material to the at least one helical elongate element.Further alternatively or additionally, a sleeve is placed around the atleast one helical elongate element, such that the elastomeric materialforms a substantially smooth layer along a radially outer edge of thesleeve, the sleeve being configured to enhance bonding of theelastomeric material to the at least one helical elongate element. Forsome applications, a rounded cross section is provided to the at leastone helical elongate element, such that the elastomeric material forms alayer having a substantially uniform thickness at an interface of theelastomeric material with the helical elongate element.

In general, in the specification and in the claims of the presentapplication, the term “proximal” and related terms, when used withreference to a device or a portion thereof, should be interpreted tomean an end of the device or the portion thereof that, when insertedinto a subject's body, is typically closer to a location through whichthe device is inserted into the subject's body. The term “distal” andrelated terms, when used with reference to a device or a portionthereof, should be interpreted to mean an end of the device or theportion thereof that, when inserted into a subject's body, is typicallyfurther from the location through which the device is inserted into thesubject's body.

The scope of the present invention includes using the apparatus andmethods described herein in anatomical locations other than the leftventricle and the aorta. Therefore, the ventricular assist device and/orportions thereof are sometimes referred to herein (in the specificationand the claims) as a blood pump.

There is therefore provided, in accordance with some applications of thepresent invention, apparatus including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured such that a proximal portion of the tube        traverses an aortic valve of the subject, and a distal portion        of the tube is disposed within a left ventricle of the subject;    -   a frame disposed within at least the distal portion of the tube;    -   a pump disposed within the frame and configured to pump blood        through the tube from the subject's left ventricle to the        subject's aorta, by pumping the blood into the tube via at least        one blood inlet opening that is defined by the tube and that is        configured to be disposed within the subject's left ventricle,        and by pumping blood out of the tube via at least one blood        outlet opening that is defined by the tube and that is        configured to be disposed within the subject's aorta; and    -   a distal-tip element configured to define a straight proximal        portion that defines a longitudinal axis, and a curved distal        portion that is shaped such as to curve in a first direction        with respect to the longitudinal axis of the straight proximal        portion before passing through an inflection point and curving        in a second direction with respect to the longitudinal axis of        the straight proximal portion, such that the curved distal        portion defines a bulge on one side of the longitudinal axis of        the straight proximal portion.

For some applications, the distal-tip element is configured to separatethe at least one blood inlet opening from a posterior wall of thesubject's left ventricle when the distal-tip element is placed againstan apex of the subject's left ventricle.

For some applications, the distal-tip element has a question-mark shape.For some applications, the distal-tip element has a tennis-racket shape.

For some applications, the curved distal portion of the distal-tipelement is shaped such that, after passing through the inflection point,the curved distal portion continues to curve such that the curved distalportion crosses back over the longitudinal axis defined by the straightproximal portion. For some applications, the curved distal portion ofthe distal-tip element is shaped such that after passing through theinflection point the curved distal portion does not cross back over thelongitudinal axis defined by the straight proximal portion.

For some applications, the blood pump includes an impeller disposed onan axial shaft, and the distal-tip element includes anaxial-shaft-receiving tube configured to receive the axial shaft of theblood pump, and a distal-tip portion configured to define the curveddistal portion of the distal-tip element.

For some applications, the distal-tip element is configured to separatethe at least one blood inlet opening from a septal wall of the subject'sleft ventricle as the distal-tip element contacts an apex of thesubject's left ventricle. For some applications, the distal-tip elementis configured such that, when distal-tip element is inserted into theleft ventricle such that the bulge bulges toward the septal wall, thenin response to the distal-tip element being pushed against the apex ofthe subject's left ventricle, the blood inlet opening gets pushed awayfrom the septal wall and toward a free wall of the subject's leftventricle. For some applications, the distal-tip element is configuredsuch that, in response to the distal-tip element being pushed againstthe apex of the subject's left ventricle, the blood inlet opening getspushed away from the septal wall and toward the free wall of thesubject's left ventricle by the straight proximal portion of thedistal-tip element pivoting about the curved distal portion of thedistal-tip element.

For some applications, the distal-tip element is configured such that,upon being deployed within a descending aorta of the subject, thedistal-tip element centers itself with respect to an aortic valve of thesubject. For some applications, the curved distal portion is shaped thatafter curving in the first direction the curved distal portion definesan elongated straight portion, before curving the in the seconddirection, such that the elongated straight portion protrudes at anangle with respect to the longitudinal axis of the proximal straightportion of the distal-tip element.

For some applications, a duckbill valve is disposed within a distal-most10 mm of the distal-tip element. For some applications, the duckbillvalve defines a wide inlet and a narrow tip that defines a slittherethrough, the duckbill valve being proximally facing, such that thewide inlet faces a distal end of the distal-tip element and such thatthe narrow tip faces away from the distal end of the distal-tip element.

For Some Applications:

the left-ventricular assist device is configured for use with aguidewire;

the distal-tip element defines a guidewire lumen; and

the left-ventricular assist device further includes a guidewire guidedisposed within the guidewire lumen at a location that is proximal tothe duckbill valve, the guidewire guide shaped to define a holetherethrough, which narrows in diameter from a proximal end of theguidewire guide to a distal end of the guidewire guide, the shape of theguidewire guide being configured to guide a tip of the guidewire towardthe slit at the narrow, proximal end of the duckbill valve, when theguidewire is inserted from a proximal end of the left-ventricular assistdevice.

For some applications, the duckbill valve is shaped to define aconverging guide portion at its proximal end, the converging guideportion converging toward the slit, such that the guide portion isconfigured to further guide the tip of the guidewire toward the slit.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller;    -   a frame configured to be disposed around the impeller;    -   a distal-tip portion disposed distally with respect to the        frame; and    -   a duckbill valve disposed entirely within a distal most 10 mm of        the distal-tip portion,    -   the duckbill valve defining a wide inlet and a narrow tip that        defines a slit therethrough,    -   the duckbill valve being proximally facing, such that the wide        inlet faces a distal end of the distal-tip portion and such that        the narrow tip faces away from the distal end of distal-tip        portion.

There is further provided, in accordance with some applications of thepresent invention, apparatus for use with a guidewire, including:

a percutaneous medical device defining a guidewire lumen that extendsfrom a proximal end of the device to a distal end of the device;

a duckbill valve disposed within a distal portion of the guidewirelumen,

-   -   the duckbill valve defining a wide inlet and a narrow tip that        defines a slit therethrough,    -   the duckbill valve being proximally facing, such that the wide        inlet faces a distal end of guidewire lumen and such that the        narrow tip faces away from the distal end of guidewire lumen;        and

a guidewire guide disposed within the guidewire lumen at a location thatis proximal to the duckbill valve, the guidewire guide shaped to definea hole therethrough, which narrows in diameter from a proximal end ofthe guidewire guide to a distal end of the guidewire guide, the shape ofthe guidewire guide being configured to guide a tip of the guidewiretoward the slit at the narrow, proximal end of the duckbill valve, whenthe guidewire is inserted from the proximal end of the percutaneousmedical device.

For some applications, the duckbill valve is shaped to define aconverging guide portion at its proximal end, the converging guideportion converging toward the slit, such that the guide portion isconfigured to further guide the tip of the guidewire toward the slit.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

a tube configured to traverse an aortic valve of a subject, such that aproximal end of the tube is disposed within an aorta of the subject anda distal end of the tube is disposed within a left ventricle of thesubject;

a frame disposed within at least a portion of the tube, the framedefining a plurality of cells, the frame being configured such that, ina non-radially-constrained configuration of the frame, the frameincludes a generally cylindrical portion, a width of each of the cellswithin the cylindrical portion as measured around a circumference of thecylindrical portion being less than 2 mm;

an inner lining that lines at least some of the cylindrical portion ofthe frame; and

an impeller disposed inside the frame such that, in anon-radially-constrained configuration of the impeller, at a location atwhich a span of the impeller is at its maximum, the impeller is disposedwithin the cylindrical portion of the frame, such that a gap between anouter edge of the impeller and the inner lining is less than 1 mm,

the impeller being configured:

-   -   to rotate such as to pump blood from the left ventricle to the        aorta, and    -   to be stabilized with respect to the frame, such that, during        rotation of the impeller, the gap between the outer edge of the        impeller and the inner lining is maintained and is substantially        constant.

For some applications, the impeller is configured to reduce a risk ofhemolysis by being stabilized with respect to the frame, relative to ifthe impeller were not stabilized with respect to the frame.

For some applications, the width of each of the cells within thecylindrical portion as measured around the circumference of thecylindrical portion is between 1.4 mm and 1.6 mm.

For some applications, the width of each of the cells within thecylindrical portion as measured around the circumference of thecylindrical portion is between 1.6 mm and 1.8 mm.

For some applications, the impeller is configured such that the gapbetween the outer edge of the impeller and the inner lining is less than0.4 mm.

For some applications:

the left-ventricular assist device further includes an axial shaft andproximal and distal radial bearings disposed, respectively, at proximaland distal ends of the frame, the axial shaft passing through theproximal and distal radial bearings;

the impeller is coupled to the axial shaft; and

the impeller is stabilized with respect to the frame by the impellerbeing held in a radially-fixed position with respect to the axial shaftand the axial shaft being rigid.

For some applications, the impeller includes bushings that are disposedaround the axial shaft, at least one of the bushings is configured to beslidable with respect to the axial shaft, and the impeller is stabilizedwith respect to the frame by a region along the axial shaft over whichthe at least one bushing is configured to be slidable with respect tothe axial shaft being coated such as to substantially prevent theimpeller from vibrating, by reducing a gap between the at least onebushing and the axial shaft.

For some applications, the impeller is stabilized with respect to theframe by substantially preventing vibration of the frame with respect tothe axial shaft by a ratio of a length of the cylindrical portion of theframe to a total length of the frame being more than 1:2.

For some applications, the ratio of the length of the cylindricalportion of the frame to the total length of the frame is more than 2:3.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured to traverse an aortic valve of a subject, such        that a proximal end of the tube is disposed within an aorta of        the subject and a distal end of the tube is disposed within a        left ventricle of the subject;    -   a frame disposed within at least a portion of the tube the frame        defining a plurality of cells, the frame being configured such        that in a non-radially-constrained configuration of the frame,        the frame includes a generally cylindrical portion;    -   proximal and distal radial bearings disposed, respectively, at        proximal and distal ends of the frame;    -   an axial shaft that passes through the proximal and distal        radial bearings;    -   an inner lining that lines at least some of the cylindrical        portion of the frame; and    -   an impeller coupled to the axial shaft inside the frame such        that, in a non-radially-constrained configuration of the        impeller, at a location at which a span of the impeller is at        its maximum, the impeller is disposed within the cylindrical        portion of the frame, such that a gap between an outer edge of        the impeller and the inner lining is less than 1 mm,    -   the impeller including bushings that are disposed around the        axial shaft, at least one of the bushings being configured to be        slidable with respect to the axial shaft, and    -   the impeller being stabilized with respect to the frame by a        region along the axial shaft over which the at least one bushing        is configured to be slidable with respect to the axial shaft        being coated such as to substantially prevent the impeller from        vibrating, by reducing a gap between the at least one bushing        and the impeller.

For some applications, the region along the axial shaft over which theat least one bushing is configured to be slidable with respect to theaxial shaft is coated with a diamond-like-carbon coating. For someapplications, the region along the axial shaft over which the at leastone bushing is configured to be slidable with respect to the axial shaftis coated with a polytetrafluoroethylene coating. For some applications,the region along the axial shaft over which the at least one bushing isconfigured to be slidable with respect to the axial shaft is coated witha polymeric sleeve. For some applications, the impeller is configured toreduce a risk of hemolysis by being stabilized with respect to theframe, relative to if the impeller were not stabilized with respect tothe frame.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured to traverse an aortic valve of a subject, such        that a proximal end of the tube is disposed within an aorta of        the subject and a distal end of the tube is disposed within a        left ventricle of the subject;    -   a frame disposed within at least a portion of the tube the frame        defining a plurality of cells, the frame being configured such        that in a non-radially-constrained configuration of the frame,        the frame includes a generally cylindrical portion;    -   proximal and distal radial bearings disposed, respectively, at        proximal and distal ends of the frame;    -   an axial shaft that passes through the proximal and distal        radial bearings;    -   an inner lining that lines at least some of the cylindrical        portion of the frame; and    -   an impeller coupled to the axial shaft inside the frame such        that, in a non-radially-constrained configuration of the        impeller, at a location at which a span of the impeller is at        its maximum, the impeller is disposed within the cylindrical        portion of the frame such that a gap between an outer edge of        the impeller and the inner lining is less than 1 mm,    -   the impeller being stabilized with respect to the frame by        substantially preventing vibration of the frame with respect to        the axial shaft, by a ratio of a length of the cylindrical        portion of the frame to a total length of the frame being more        than 1:2.

For some applications, the ratio of the length of the cylindricalportion of the frame to the total length of the frame is more than 2:3.

For some applications, the impeller is configured to reduce a risk ofhemolysis by being stabilized with respect to the frame, relative to ifthe impeller were not stabilized with respect to the frame.

There is further provided, in accordance with some applications of thepresent invention, a method, including:

manufacturing an impeller by:

-   -   forming a structure having first and second bushings at proximal        and distal ends of the structure, the first and second bushings        being connected to one another by at least one elongate element;    -   causing the at least one elongate element to radially expand and        form at least one helical elongate element, at least partially        by axially compressing the structure; and    -   coupling an elastomeric material to the at least one helical        elongate element, such that the at least one helical elongate        element with the elastomeric material coupled thereto defines a        blade of the impeller, the coupling being performed such that a        layer of the material is disposed around a radially outer edge        of the at least one helical elongate element, the layer of        material forming the effective edge of the impeller blade;    -   the method including performing a step to enhance bonding of the        elastomeric material to the at least one helical elongate        element in a manner that does not cause a protrusion from the        effective edge of the impeller blade.

For some applications, manufacturing the impeller further includesplacing a spring within the structure such that the spring extends fromthe first bushing to the second bushing, and coupling the elastomericmaterial to the at least one helical elongate element includes forming afilm of the elastomeric material that extends from the at least onehelical elongate element to the spring.

For Some Applications:

forming the structure includes forming a structure having first andsecond bushings at proximal and distal ends of the structure, the endportions being connected to one another by two elongate elements;

causing the at least one elongate element to radially expand and form atleast one helical elongate element includes causing the two elongateelements to radially expand and form two helical elongate elements; and

coupling the elastomeric material to the at least one helical elongateelement includes coupling the elastomeric material to the two helicalelongate elements, such that the two helical elongate elements with theelastomeric material coupled thereto define a blade of the impeller.

For Some Applications:

forming the structure includes forming a structure having first andsecond bushings at proximal and distal ends of the structure, the endportions being connected to one another by three or more elongateelements;

causing the at least one elongate element to radially expand and form atleast one helical elongate element includes causing the three elongateelements to radially expand and form three or more helical elongateelements; and

coupling the elastomeric material to the at least one helical elongateelement includes coupling the elastomeric material to the three or morehelical elongate elements, such that each of the three or more helicalelongate elements with the elastomeric material coupled thereto definesa respective blade of the impeller.

For some applications, causing the at least one elongate element toradially expand and form at least one helical elongate element furtherincludes twisting the structure.

For some applications, performing the step to enhance bonding of theelastomeric material to the at least one helical elongate elementincludes placing sutures within grooves defined by the at least onehelical elongate element, such that the sutures do not protrude from theradially outer edge of the helical elongate element, the sutures beingconfigured to enhance bonding of the elastomeric material to the atleast one helical elongate element.

For some applications, performing the step to enhance bonding of theelastomeric material to the at least one helical elongate elementincludes placing a tightly-wound coil around the at least one helicalelongate element, such that the elastomeric material forms asubstantially smooth layer along a radially outer edge of the coil, thecoil being configured to enhance bonding of the elastomeric material tothe at least one helical elongate element.

For some applications, performing the step to enhance bonding of theelastomeric material to the at least one helical elongate elementincludes placing a sleeve around the at least one helical elongateelement, such that the elastomeric material forms a substantially smoothlayer along a radially outer edge of the sleeve, the sleeve beingconfigured to enhance bonding of the elastomeric material to the atleast one helical elongate element.

For some applications, performing the step to enhance bonding of theelastomeric material to the at least one helical elongate elementincludes providing a rounded cross section to the at least one helicalelongate element, such that the elastomeric material forms a layerhaving a substantially uniform thickness at an interface between theelastomeric material and the helical elongate element.

There is further provided, in accordance with some applications of thepresent invention, apparatus for use with a delivery catheter including:

a blood pump including:

-   -   an impeller configured to pump blood through a subject's body;    -   a frame disposed around the impeller,    -   the impeller and frame defining non-radially-constrained        configurations in which the impeller is configured to pump blood        within the subject's body, and defining radially-constrained        configurations in which the impeller and frame are inserted and        removed from the subject's body using a delivery catheter,    -   the frame defining struts having a structure that is such that,        as the frame transitions from a proximal end of the frame toward        a center of the frame, the struts pass through junctions, at        which the two struts branch from a single strut, in a Y-shape;    -   the structure of the struts of the frame being configured such        that, in response to a distal end of the delivery catheter and        the frame being moved into overlapping positions with respect to        each other, the frame is configured to assume its        radially-constrained configuration by becoming axially        elongated, and is configured to cause the impeller to assume its        radially constrained configuration by becoming axially        elongated.

For some applications, the structure of the struts of the frame isconfigured such that, in response to a distal end of the deliverycatheter and the frame being moved into overlapping positions withrespect to each other, the frame is configured to assume itsradially-constrained configuration by becoming axially elongated, and isconfigured to cause the impeller to assume its radially constrainedconfiguration by becoming axially elongated, by the pairs of struts thatbranch from the junctions being configured to pivot about the junctionand move closer to each other such as to close.

For some applications, in its radially-non-constrained configuration,the frame defines a proximal conical portion, a distal conical portion,and a cylindrical portion between the proximal conical portion and thedistal conical portion.

For some applications, within the cylindrical portion of the frame, astrut density of the frame is constant.

For some applications, a density of the struts increases from theproximal conical portion to the cylindrical portion, and from the distalconical portion to the cylindrical portion.

For some applications, during operation of the blood pump, the impelleris configured to move with respect to the frame, and a range of movementof the impeller is such that at least a portion of the impeller isdisposed within the proximal conical portion of the frame during atleast some of the operation of the blood pump, and at least a portion ofthe impeller is disposed within the cylindrical portion of the frameduring at least some of the operation of the blood pump.

For some applications, throughout the operation of the blood pump, at alocation at which a span of the impeller is at its maximum, the impelleris configured to be disposed within the cylindrical portion of theframe.

For some applications, a width of each of the cells within thecylindrical portion as measured around a circumference of thecylindrical portion is less than 2 mm.

For some applications, the width of each of the cells within thecylindrical portion as measured around the circumference of thecylindrical portion is between 1.4 mm and 1.6 mm.

For some applications, the width of each of the cells within thecylindrical portion as measured around the circumference of thecylindrical portion is between 1.6 mm and 1.8 mm.

There is further provided, in accordance with some applications of thepresent invention, a method, including:

manufacturing a housing for an impeller of a blood pump by:

-   -   placing an inner lining around a mandrel;    -   placing, around the inner lining, a cylindrical portion of a        frame, the cylindrical portion of the frame including struts        that define a generally cylindrical shape;    -   placing a distal portion of an elongate tube around at least a        portion of the frame, the tube including a proximal portion that        defines at least one blood outlet opening;    -   while the distal portion is disposed around at least the portion        of the frame, heating the inner lining, the frame and the distal        portion of the elongate tube via the mandrel; and    -   while heating the inner lining, the frame and the distal portion        of the elongate tube, applying pressure from outside the distal        portion of the elongate tube, such as to cause the distal        portion of the elongate tube to conform with a structure of the        struts of the frame, and such as to cause the inner lining and        the distal portion of the elongate tube to become coupled to the        frame.

For some applications, the method further includes, subsequent tocausing the inner lining and the distal portion of the elongate tube tobecome coupled to the frame, shaping a distal end of the frame to definea widened inlet.

For some applications, the method further includes, subsequent tocausing the inner lining and the distal portion of the elongate tube tobecome coupled to the frame, shaping a portion of the frame to form aconverging region, such that the frame defines a narrowing in a vicinityof a location within the frame that is configured to house the impeller.

For some applications, placing the distal portion of the elongate tubearound at least a portion of the frame includes placing the distalportion of the elongate tube around the entire cylindrical portion ofthe frame, such the distal portion of the elongate tube overlaps withthe entire inner lining.

For Some Applications:

the inner lining and the elongate tube include an inner lining andelongate tube that are made from different materials from each other,and a thermoforming temperature of a material from which the innerlining is made is higher than a thermoforming temperature of a materialfrom which the elongate tube is made, and

heating the inner lining, the frame and the distal portion of theelongate tube includes heating the inner lining, the frame and thedistal portion of the elongate tube to a temperature that is above thethermoforming temperature of the material from which the elongate tubeis made and below the thermoforming temperature of the material fromwhich the inner lining is made.

For some applications, applying pressure from outside the distal portionof the elongate tube includes applying pressure from outside the distalportion of the elongate tube using an outer tube that is made ofsilicone.

For some applications, applying pressure from outside the distal portionof the elongate tube, such as to cause the inner lining and the distalportion of the elongate tube to become coupled to the frame, includescoupling the inner lining to an inner surface of the cylindrical portionof the frame, such that the inner lining forms a substantiallycylindrical tube.

For some applications, the struts within the cylindrical portion of theframe are shaped to define cells, and a width of each of the cells asmeasured around a circumference of the cylindrical portion is less than2 mm.

For some applications, placing the distal portion of the elongate tubearound at least a portion of the frame includes placing the distalportion of the elongate tube around only a portion of the cylindricalportion of the frame, such the distal portion of the elongate tube doesnot overlap with the entire inner lining.

For some applications, placing the distal portion of the elongate tubearound only a portion of the cylindrical portion of the frame includespreventing radial expansion of the portion of the cylindrical portion ofthe frame around which the distal portion of the elongate tube isplaced, thereby causing the portion of the cylindrical portion of theframe around which the distal portion of the elongate tube is placed tobe narrower than a portion of the cylindrical portion of the framearound which the elongate tube is not placed.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller;    -   a frame configured to be disposed around the impeller, the frame        including struts;    -   an inner lining disposed inside the frame;    -   an outer covering material coupled to the inner coupling        material from outside the frame at discrete coupling regions        along a length of the frame,    -   a density of the struts of the frame at the coupling regions        being less than a density of the struts of the frame at other        regions along the length of the frame.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller;    -   a frame configured to be disposed around the impeller, the frame        including struts,

and a cylindrical portion of the frame being shaped to define acylindrical cross-section;

-   -   an inner lining disposed inside the frame;    -   an outer covering material coupled to the inner coupling        material from outside the frame, the outer covering material        being disposed around only a portion of the cylindrical portion        of the frame and the outer covering material being configured to        restrict radial expansion of the portion of the cylindrical        portion of the frame around which the outer covering material is        placed, such that the portion of the cylindrical region of the        frame around which the distal portion of the outer covering        material is placed is narrower than a portion of the cylindrical        region of the frame around which the outer covering material is        not placed.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller;    -   a frame configured to be disposed around the impeller, the frame        being configured to define a cylindrical portion that has a        substantially cylindrical cross-section;    -   a covering material that is coupled to the cylindrical portion        of the frame, such that a distal end of the cylindrical portion        of the frame defines a blood inlet opening, the impeller being        configured to be disposed within 15 mm of the blood inlet        opening throughout operation of the impeller,    -   a portion of the frame being shaped such as to reduce turbulence        that is generated as blood flows from the blood inlet opening        toward the impeller.

For some applications, the portion of the frame includes a widenedportion of the frame.

For some applications, the portion of the frame includes a portion ofthe frame that is shaped to converge toward the impeller.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic illustrations of a ventricular assistdevice, a distal end of which is configured to be placed in a subject'sleft ventricle, in accordance with some applications of the presentinvention;

FIGS. 2A, 2B, 2C, 2D, 2E, and 2F are schematic illustrations of a framethat houses an impeller of a ventricular assist device, in accordancewith some applications of the present invention;

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, 3I, 3J, and 3K are schematicillustrations of an impeller of a ventricular assist device or a portionthereof, in accordance with some applications of the present invention;

FIG. 4 is a schematic illustration of an impeller disposed inside aframe of a ventricular assist device, in accordance with someapplications of the present invention;

FIGS. 5A and 5B are schematic illustrations of the impeller and theframe of the ventricular assist device, respectively innon-radially-constrained and radially-constrained states thereof, inaccordance with some applications of the present invention;

FIG. 5C is a schematic illustration of a typical bearing assembly thatis used in prior art axial impeller-based blood pumps;

FIGS. 6A and 6B are schematic illustrations of a ventricular assistdevice at respective stages of a motion cycle of the impeller of theventricular assist device with respect to the frame of the ventricularassist device, in accordance with some applications of the presentinvention;

FIG. 6C is a schematic illustration of a distal-tip element thatincludes an axial-shaft-receiving tube and a distal-tip portion of aventricular assist device, in accordance with some applications of thepresent invention;

FIG. 6D is a schematic illustration of an axial shaft of a ventricularassist device that is at least partially covered or coated, such as toreduce a gap between the axial shaft and a bushing of an impeller thatslides over the axial shaft, in accordance with some applications of thepresent invention;

FIG. 6E is a schematic illustration of an axial shaft of a ventricularassist device and a bushing of an impeller that slides over the axialshaft, the axial shaft and the impeller bushing being configured toprevent rotational motion of the impeller bushing with respect to theaxial shaft, in accordance with some applications of the presentinvention;

FIGS. 6F and 6G are schematic illustrations of an impeller housingconfigured to provide a gap between the impeller and the housing thatvaries over the course of a subject's cardiac cycle, in accordance withsome applications of the present invention;

FIG. 7 is a schematic illustration of a motor unit of a ventricularassist device, in accordance with some applications of the presentinvention;

FIGS. 8A and 8B are schematic illustrations of a motor unit of aventricular assist device, in accordance with some applications of thepresent invention;

FIG. 9 is a graph indicating variations in the length of a drive cableof a ventricular assist device as a pressure gradient against which theimpeller of the blood pump varies, as measured in experiments performedby the inventors of the present application;

FIGS. 10A, 10B, and 10C are schematic illustrations of a drive cable ofa ventricular assist device, in accordance with some applications of thepresent invention;

FIGS. 10D, 10E, and 1OF are schematic illustrations of the drive cableand an axial shaft of the ventricular assist device, in accordance withsome applications of the present invention;

FIGS. 11A and 11B are schematic illustrations of an impeller that iscoupled to an axial shaft at the distal end of the impeller and that isnot coupled to the axial shaft at the proximal end of the impeller, inaccordance with some applications of the present invention;

FIG. 11C is a schematic illustration of coupling portions forfacilitating the crimping of the impeller of FIGS. 11A and 11B;

FIG. 12A is a graph showing the relationship between the pressuregradient against which the impeller is pumping and the pitch of theimpeller when the impeller is configured as shown in FIG. 11A;

FIG. 12B is a graph showing pressure-flow curves for impellers havingrespective pitches, in accordance with some applications of the presentinvention;

FIGS. 13A, 13B, and 13C are schematic illustrations of a procedure forpurging a drive cable and/or radial bearings of a ventricular assistdevice, in accordance with some applications of the present invention;

FIG. 13D is a schematic illustration of a ventricular assist device thatincludes an inflatable portion (e.g., a balloon) disposed around itsdistal-tip portion, the inflatable portion being configured to beinflated by a fluid that is used for purging the drive cable of thedevice, in accordance with some applications of the present invention;

FIG. 13E is a schematic illustration of a technique for reducingfrictional forces between a drive cable and an outer tube in which thedrive cable rotates and/or for reducing frictional forces at radialbearings of a ventricular assist device, in accordance with someapplications of the present invention;

FIGS. 14A, 14B, and 14C are schematic illustrations of a statorconfigured to be disposed inside a tube of a ventricular assist device,proximal to a frame in which the impeller of the ventricular assistdevice is disposed, in accordance with some applications of the presentinvention;

FIGS. 15A, 15B, 15C, 15D, and 15E are schematic illustration of a statorthat is built into a tube of a ventricular assist device, in accordancewith some applications of the present invention;

FIGS. 16A and 16B are schematic illustrations of a ventricular assistdevice that includes one or more ventricular blood-pressure-measurementtubes, in accordance with some applications of the present invention;

FIGS. 16C and 16D are schematic illustrations of a ventricular assistdevice having an aortic blood pressure measurement channel within adelivery catheter, in accordance with some applications of the presentinvention;

FIG. 16E is a schematic illustration of a ventricular assist device thatincludes one or more sensors that are disposed on an outer surface of atube of the device, in accordance with some applications of the presentinvention;

FIGS. 17A, 17B, 17C, and 17D are schematic illustrations of aventricular assist device that includes a pitot tube that is configuredto measure blood flow through a tube of the device, in accordance withsome applications of the present invention;

FIG. 18 is a schematic illustration of a ventricular assist device thatincludes coronary artery tubes and/or wires, in accordance with someapplications of the present invention;

FIGS. 19A, 19B, 19C, 19D, 19E, 19F, 19G, and 19H are schematicillustrations of a ventricular assist device that includes an innerlining on the inside of the frame that houses the impeller, inaccordance with some applications of the present invention;

FIGS. 20A, 20B, and 20C are schematic illustrations of a ventricularassist device that includes an inflatable portion (e.g., a balloon)disposed around its distal-tip portion, in accordance with someapplications of the present invention;

FIG. 21 is a schematic illustration of a ventricular assist device beingplaced inside a subject's left ventricle, with a transversecross-sectional view of the left ventricle being illustrated, inaccordance with some applications of the present invention;

FIG. 22A, 22B, 22C, and 22D are schematic illustrations of a distal-tipelement of a ventricular assist device that is at least partially curvedsuch as to define a question-mark shape or a tennis-racket shape, inaccordance with some applications of the present invention;

FIGS. 23A and 23B are schematic illustrations of the ventricular assistdevice of FIG. 22D disposed inside a subject's left ventricle, inaccordance with some applications of the present invention;

FIGS. 24A, 24B, and 24C are schematic illustrations of a distal-tipelement that is configured to center itself with respect to a subject'saortic valve, in accordance with some applications of the presentinvention;

FIGS. 25A, 25B, 25C, 25D, and 25E are schematic illustrations of aventricular assist device that includes a tube that is configured tobecome curved when blood is pumped through the tube, in accordance withsome applications of the present invention;

FIG. 25F is a schematic illustration of a ventricular assist device thatincludes a curved element that is made of a shape-memory material andthat is configured to provide a portion of the ventricular assist devicewith a predefined curvature, in accordance with some applications of thepresent invention;

FIGS. 26A, 26B, 26C, 26D, 26E, and 26F are schematic illustrations of adistal-tip element of a ventricular assist device that is at leastpartially curved, in accordance with some applications of the presentinvention;

FIGS. 27A, 27B, and 27C are schematic illustrations of an atraumaticprojection that includes a closed ellipse or a closed circle and that isconfigured to extend distally from a distal-tip element of a ventricularassist device, in accordance with some applications of the presentinvention;

FIG. 28A is a schematic illustration of a duckbill valve and guidewireguide disposed at the distal end of an atraumatic tip, in accordancewith some applications of the present invention;

FIGS. 28B and 28C are schematic illustration of respective views of theduckbill valve of FIG. 28A, in accordance with some applications of thepresent invention;

FIGS. 28D and 28E are schematic illustration of respective views of theguidewire guide of FIG. 28A, in accordance with some applications of thepresent invention;

FIG. 29 is a schematic illustration of a delivery catheter that includesa sheath configured to facilitate reinsertion of a guidewire through apercutaneous puncture, in accordance with some applications of thepresent invention;

FIG. 30 is a schematic illustration of a ventricular assist device thatincludes two impellers, in accordance with some applications of thepresent invention;

FIG. 31 is a schematic illustration of a ventricular assist device thatincludes two impellers, in accordance with some applications of thepresent invention;

FIGS. 32A, 32B, 32C, 32D, and 32E are schematic illustration of aventricular assist device that is configured to assist the functioningof the right heart of a subject, in accordance with some applications ofthe present invention; and

FIG. 33 is a schematic illustration of a venous assist device, inaccordance with some applications of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIGS. 1A, 1B, and 1C, which are schematicillustrations of a ventricular assist device 20, a distal end of whichis configured to be disposed in a subject's left ventricle 22, inaccordance with some applications of the present invention. FIGS. 1Ashows an overview of the ventricular assist device system including acontrol console 21, and a motor unit 23, FIG. 1B shows the ventricularassist device being inserted into the subject's left ventricle, and FIG.1C shows a pump portion 27 of the ventricular assist device in greaterdetail. The ventricular assist device includes a tube 24, whichtraverses an aortic valve 26 of the subject, such that a proximal end 28of the tube is disposed in an aorta 30 of the subject and a distal end32 of the tube is disposed within left ventricle 22. Tube 24 (which issometimes referred to herein as a “blood-pump tube”) is typically anelongate tube, an axial length of the tube typically being substantiallylarger than its diameter. The scope of the present invention includesusing the apparatus and methods described herein in anatomical locationsother than the left ventricle and the aorta. Therefore, the ventricularassist device and/or portions thereof are sometimes referred to herein(in the specification and the claims) as a blood pump.

For some applications, the ventricular assist device is used to assistthe functioning of a subject's left ventricle during a percutaneouscoronary intervention. In such cases, the ventricular assist device istypically used for a period of up to 10 hours (e.g., up to six hours),during a period in which there is risk of developing hemodynamicinstability (e.g., during or immediately following the percutaneouscoronary intervention). Alternatively or additionally, the ventricularassist device is used to assist the functioning of a subject's leftventricle for a longer period (e.g., for example, 2-20 days, e.g., 4-14days) upon a patient suffering from cardiogenic shock, which may includeany low-cardiac-output state (e.g., acute myocardial infarction,myocarditis, cardiomyopathy, post-partum, etc.). For some applications,the ventricular assist device is used to assist the functioning of asubject's left ventricle for yet a longer period (e.g., several weeks ormonths), e.g., in a “bridge to recovery” treatment. For some suchapplications, the ventricular assist device is permanently orsemi-permanently implanted, and the impeller of the ventricular assistdevice is powered transcutaneously, e.g., using an external antenna thatis magnetically coupled to the impeller.

As shown in FIG. 1B, which shows steps in the deployment of theventricular assist device in the left ventricle, typically the distalend of the ventricular assist device is guided to the left ventricleover a guidewire 10. During the insertion of the distal end of thedevice to the left ventricle, a delivery catheter 143 is disposed overthe distal end of the device. Once the distal end of the device isdisposed in the left ventricle, the delivery catheter is typicallyretracted to the aorta, and the guidewire is withdrawn from thesubject's body. The retraction of the delivery catheter typically causesself-expandable components of the distal end of the device to assumenon-radially-constrained configurations, as described in further detailhereinbelow. Typically, the ventricular assist device is inserted intothe subject's body in order to provide an acute treatment to thesubject. For some applications, in order to withdraw the leftventricular device from the subject's body at the end of the treatment,the delivery catheter is advanced over the distal end of the device,which causes the self-expandable components of the distal end of thedevice to assume radially-constrained configurations. Alternatively oradditionally, the distal end of the device is retracted into thedelivery catheter which causes the self-expandable components of thedistal end of the device to assume radially-constrained configurations.

For some applications (not shown), the ventricular assist device and/ordelivery catheter 143 includes an ultrasound transducer at its distalend and the ventricular assist device is advanced toward the subject'sventricle under ultrasound guidance.

Referring now to FIG. 1C, which shows pump portion 27 of ventricularassist device 20 in greater detail, typically, an impeller 50 isdisposed within a distal portion 102 of tube 24 and is configured topump blood from the left ventricle into the aorta by rotating. The tubetypically defines one or more blood inlet openings 108 at the distal endof the tube, via which blood flows into the tube from the leftventricle, during operation of the impeller. For some applications,proximal portion 106 of the tube defines one or more blood outletopenings 109, via which blood flows from the tube into the ascendingaorta, during operation of the impeller.

For some applications, control console 21 (shown in FIG. 1A), whichtypically includes a computer processor 25, drives the impeller torotate. For example, the computer processor may control a motor 74(shown in FIG. 7), which is disposed within motor unit 23 (shown in FIG.1A) and which drives the impeller to rotate via a drive cable 130 (shownin FIG. 7). For some applications, the computer processor is configuredto detect a physiological parameter of the subject (such asleft-ventricular pressure, cardiac afterload, rate of change ofleft-ventricular pressure, etc.) and to control rotation of the impellerin response thereto, as described in further detail hereinbelow.Typically, the operations described herein that are performed by thecomputer processor, transform the physical state of a memory, which is areal physical article that is in communication with the computerprocessor, to have a different magnetic polarity, electrical charge, orthe like, depending on the technology of the memory that is used.Computer processor 25 is typically a hardware device programmed withcomputer program instructions to produce a special-purpose computer. Forexample, when programmed to perform the techniques described herein,computer processor 25 typically acts as a special-purpose,ventricular-assist computer processor and/or a special-purpose,blood-pump computer processor.

For some applications, a purging system 29 (shown in FIG. 1A) drives afluid (e.g., a glucose solution) to pass through portions of ventricularassist device 20, for example, in order to cool portions of the deviceand/or in order to wash debris from portions of the device. Purgingsystem 29 is described in further detail hereinbelow.

Typically, along distal portion 102 of tube 24, a frame 34 is disposedwithin the tube around impeller 50. The frame is typically made of ashape-memory alloy, such as nitinol. For some applications, theshape-memory alloy of the frame is shape set such that at least aportion of the frame (and thereby distal portion 102 of tube 24) assumesa generally circular, elliptical, or polygonal cross-sectional shape inthe absence of any forces being applied to distal portion 102 of tube24. By assuming its generally circular, elliptical, or polygonalcross-sectional shape, the frame is configured to hold the distalportion of the tube in an open state. Typically, during operation of theventricular assist device, the distal portion of the tube is configuredto be placed within the subject's body, such that the distal portion ofthe tube is disposed at least partially within the left ventricle.

For some applications, along proximal portion 106 of tube 24, the frameis not disposed within the tube, and the tube is therefore not supportedin an open state by frame 34. Tube 24 is typically made of ablood-impermeable collapsible material. For example, tube 24 may includepolyurethane, polyester, and/or silicone. Alternatively or additionally,the tube is made of polyethylene terephthalate (PET) and/or polyetherblock amide (e.g., PEBAX®). For some applications (not shown), the tubeis reinforced with a reinforcement structure, e.g., a braidedreinforcement structure, such as a braided nitinol tube. Typically, theproximal portion of the tube is configured to be placed such that it isat least partially disposed within the subject's ascending aorta. Forsome applications, the proximal portion of the tube traverses thesubject's aortic valve, passing from the subject's left ventricle intothe subject's ascending aorta, as shown in FIG. 1B. As describedhereinabove, the tube typically defines one or more blood inlet openings108 at the distal end of the tube, via which blood flows into the tubefrom the left ventricle, during operation of the impeller. For someapplications, the proximal portion of the tube defines one or more bloodoutlet openings 109, via which blood flows from the tube into theascending aorta, during operation of the impeller. Typically, the tubedefines a plurality of blood outlet openings 109, for example, betweentwo and eight blood outlet openings (e.g., between two and four bloodoutlet openings). During operation of the impeller, the pressure of theblood flow through the tube typically maintains the proximal portion ofthe tube in an open state. For some applications, in the event that, forexample, the impeller malfunctions, the proximal portion of the tube isconfigured to collapse inwardly, in response to pressure outside of theproximal portion of the tube exceeding pressure inside the proximalportion of the tube. In this manner, the proximal portion of the tubeacts as a safety valve, preventing retrograde blood flow into the leftventricle from the aorta.

Referring again to FIG. 1C, for some applications, frame 34 is shapedsuch that the frame defines a proximal conical portion 36, a centralcylindrical portion 38, and a distal conical portion 40. Typically, theproximal conical portion is such that the narrow end of the cone isproximal with respect to the wide end of the cone. Further typically,the distal conical portion is such that the narrow end of the cone isdistal with respect to the wide end of the cone. For some applications,tube 24 extends to the end of cylindrical portion 38 (or slightlyproximal or distal thereof), such that the distal end of the tubedefines a single axially-facing blood inlet opening 108, as shown inFIG. 1C. For some applications, within at least a portion of frame 34,an inner lining 39 lines the frame, as described hereinbelow withreference to FIGS. 19A-H. In accordance with respective applications,the inner lining partially overlaps or fully overlaps with tube 24 overthe portion of the frame that the inner lining lines. For suchapplications, the distal end of the inner lining defines a singleaxially-facing blood inlet opening 108. For some applications (notshown), tube 24 extends to the end of distal conical portion 40, and thetube defines one or more lateral blood inlet openings (not shown), e.g.,as described in US 2019/0209758 to Tuval, which is incorporated hereinby reference. For such applications, the tube typically defines two tofour lateral blood inlet openings.

Typically, tube 24 includes a conical proximal portion 42 and acylindrical central portion 44. The proximal conical portion istypically such that the narrow end of the cone is proximal with respectto the wide end of the cone. Typically, blood outlet openings 109 aredefined by tube 24, such that the openings extend at least partiallyalong the proximal conical section of tube 24. For some suchapplications, the blood outlet openings are teardrop-shaped, as shown inFIG. 1C. Typically, the teardrop-shaped nature of the blood outletopenings in combination with the openings extending at least partiallyalong the proximal conical section of tube 24 causes blood to flow outof the blood outlet openings along flow lines that are substantiallyparallel with the longitudinal axis of tube 24 at the location of theblood outlet openings.

As described hereinabove, for some applications (not shown), the tubeextends to the end of distal conical portion 40 of frame 34. For suchapplications, the tube typically defines a distal conical portion, withthe narrow end of the cone being distal with respect to the wide end ofthe cone. For some applications (not shown), the diameter of tube 24changes along the length of the central portion of the tube, such thatthe central portion of the tube has a frustoconical shape. For example,the central portion of the tube may widen from its proximal end to isdistal end, or may narrow from its proximal end to its distal end. Forsome applications, at its proximal end, the central portion of the tubehas a diameter of between 5 and 7 mm, and at its distal end, the centralportion of the tube has a diameter of between 8 and 12 mm.

Again referring to FIG. 1C, the ventricular assist device typicallyincludes a distal-tip element 107 that is disposed distally with respectto frame 34 and that includes an axial-shaft-receiving tube 126 and adistal-tip portion 120, both of which are described in further detailhereinbelow.

Reference is now made to FIGS. 2A, 2B, 2C, 2D, 2E, and 2F, which areschematic illustrations of frame 34 that houses an impeller ofventricular assist device 20, in accordance with some applications ofthe present invention. As described hereinabove, frame 34 is typicallymade of a shape-memory alloy, such as nitinol, and the shape-memoryalloy of the frame is shape set such that the frame (and thereby tube24) assumes a generally circular, elliptical, or polygonalcross-sectional shape in the absence of any forces being applied to tube24. By assuming its generally circular, elliptical, or polygonalcross-sectional shape, the frame is configured to hold the distalportion of the tube in an open state.

Typically, the frame is a stent-like frame, in that it comprises strutsthat, in turn, define cells. Further typically, the frame is coveredwith tube 24, and/or covered with an inner lining 39, describedhereinbelow, with reference to FIGS. 19A-H. As described hereinbelow,for some applications impeller 50 undergoes axial back-and-forth motionwith respect to frame 34. Typically over the course of the motion of theimpeller with respect to the frame the location of the portion of theimpeller that defines the maximum span of the impeller is disposedwithin cylindrical portion 38 of frame 34. In some cases, if the cellsof the cylindrical portion 38 of frame 34 are too large, then tube 24,and/or inner lining 39 gets stretched between edges of the cells, suchthat the tube 24, and/or inner lining 39 does not define a circularcross-section. For some applications, if this occurs in the region inwhich the portion of the impeller that defines the maximum span of theimpeller is disposed, this results in a non-constant gap between theedges of the impeller blades and tube 24 (and/or inner lining) at thatlocation, over the course of a rotation cycle of the impeller. For someapplications, this may lead to increased hemolysis relative to if therewere a constant gap between the edges of the impeller blades and tube 24(and/or inner lining) at that location, over the course of the rotationcycle of the impeller.

Referring to FIG. 2A, at least partially in view of the issues describedin the above paragraph, within cylindrical portion 38 of frame 34, theframe defines a large number of relatively small cells. Typically, whenthe frame is disposed in its non-radially-constrained configuration, themaximum cell width CW of the each of the cells (i.e., the distance fromthe inner edge of the strut at the central junction on one side of thecell to the inner edge of the strut at the central junction on the otherside of the cell, as measured around the circumference of cylindricalportion 38) within the cylindrical portion of the frame is less than 2mm, e.g., between 1.4 mm and 1.6 mm, or between 1.6 and 1.8 mm. Sincethe cells are relatively small, the tube 24 (and/or inner lining)defines a substantially circular cross-section within the cylindricalportion of the frame.

Still referring to FIG. 2A, and starting from the proximal end of theframe (which is to the left of the figure), typically the frame definesthe following portions (a) coupling portion 31 via which the frame iscoupled to a proximal bearing 116 (shown in FIG. 4) of the ventricularassist device, (b) proximal conical portion 36, (c) cylindrical portion38, (d) distal conical portion 40, and (e) distal strut junctions 33. Asillustrated, as the frame transitions from a proximal end of the frametoward the center of the frame (e.g., as the frame transitions throughcoupling portion 31, through proximal conical portion 36, and tocylindrical portion 38), struts 37 of the frame pass through junctions35, at which the two struts branch from a single strut, in a Y-shape. Asdescribed in further detail hereinbelow, typically frame 34 is placed ina radially-constrained (i.e., crimped) configuration within deliverycatheter 143 by the frame being axially elongated. Moreover, the frametypically transmits its radial narrowing to the impeller, and theimpeller becomes radially constrained by becoming axially elongatedwithin the frame. For some applications, the struts of the frame beingconfigured in the manner described above facilitates transmission ofaxial elongation from the delivery catheter (or other device that isconfigured to crimp the frame) to the frame, which in turn facilitatestransmission of axial elongation to the impeller. This is because thepairs of struts that branch from each of junctions 35 are configured topivot about the junction and move closer to each other such as to close.

Still referring to FIG. 2A, for some applications distal strut junctions33 are maintained in open states when the frame is coupled to axialshaft 92 (shown in FIG. 2D), in order for the impeller to be placedwithin the frame via the distal end of the frame. Subsequently, thedistal strut portions are closed around the outside of a distal bearing118, as described in further detail hereinbelow with reference to FIGS.5A-B. For some applications, a proximal end of distal-tip element 107(shown in FIG. 1C) holds the distal strut portions in their closedconfigurations around the outside of distal bearing 118.

Typically, when disposed in its non-radially constrained configuration,frame 34 has a total length of more than 25 mm (e.g., more than 30 mm),and/or less than 50 mm (e.g., less than 45 mm), e.g., 25-50 mm, or 30-45mm. Typically, when disposed in its radially-constrained configuration(within delivery catheter 143), the length of the frame increases bybetween 2 and 5 mm. Typically, when disposed in its non-radiallyconstrained configuration, the cylindrical portion of frame 34 has alength of more than 10 mm (e.g., more than 12 mm), and/or less than 25mm (e.g., less than 20 mm), e.g., 10-25 mm, or 12-20 mm. For someapplications, a ratio of the length of the cylindrical portion of theframe to the total length of the frame is more than 1:4 and/or less than1:2, e.g., between 1:4 and 1:2.

Reference is now made to FIG. 2B, which is a schematic illustration of apump portion of ventricular assist device 20, at least a portion ofcylindrical portion 38 of frame 34 of the ventricular assist devicehaving a helical structure 55, in accordance with some applications ofthe present invention. For some applications, at least a portion ofcylindrical portion 38 of frame 34 of the ventricular assist device hasa helical structure 55, in order for the tube 24 (and/or inner lining)to define a substantially circular cross-section within the cylindricalportion of the frame, e.g., for the reasons provided hereinabove.

Reference is now made to FIG. 2C, which is a schematic illustration offrame 34, the frame transitioning from its ends to its maximum diameter(i.e., the cylindrical portion of the frame) over a relatively shortdistance D. Typically, this results in the ratio of the cylindricalportion of the frame to the total length of the frame being greater thanthat described hereinabove. For example, the ratio of the cylindricalportion of the frame to the total length of the frame may be more than1:2 or more than 2:3. Further typically, this results in the angle atwhich the frame widens within the conical portion being greater than ifthe cylindrical portion has a shorter relative length, ceteris paribus.For some applications, in turn, this reduces vibration of the frameduring rotation of the impeller. As described hereinabove, in order toreduce hemolysis, it is typically desirable to maintain a constant gapbetween the edges of the impeller blades and tube 24 (and/or innerlining 39). Therefore, it is typically desirable to reduce vibration ofthe frame with respect to the impeller.

Reference is now made to FIG. 2D, which is a schematic illustration of apump portion of a ventricular assist device that includes an inflatableimpeller housing 60, in accordance with some applications of the presentinvention. For some applications, rather than having frame 34surrounding the impeller, the inflatable housing surrounds the impeller.For some applications, at least in the region of the housing thatsurrounds the impeller, the frame is configured to define an innercircular cross-section, such that there is a constant gap between theedges of the impeller blades and the inner wall of the housing, over thecourse of the rotation cycle of the impeller.

Typically, for applications as shown in FIG. 2D, proximal and distalbearing frames 61 are disposed inside the inflatable impeller housing.The bearing frames are configured to act as radial bearings with respectto axial shaft 92 (described hereinbelow) to which impeller 50 iscoupled. For some applications, the impeller housing is made of aflexible and inflatable material. The impeller housing is typicallyinserted into the left ventricle in a deflated state, and is inflatedonce disposed inside the left ventricle, such as to assume its deployedshape. Tube 24 typically extends proximally from the inflatable impellerhousing. For some applications, tubes 63 pass along tube 24 (e.g., aninner surface or an outer surface of the tube), and the inflatablehousing is inflated via the tubes. For some applications, the impellerhousing is inflated with saline and/or a different solution (e.g., aglucose solution). For some applications, the inflatable impellerhousing defines one or more blood inlet openings 108.

Reference is now made to FIG. 2E and 2F, which are schematicillustrations of flattened profiles of frame 34, the frame beinggenerally configured as shown in FIG. 2A, in accordance with someapplications of the present invention. Frame 34 is typically laser cutfrom a tube of a shape memory alloy, such as nitinol. The profiles shownin FIGS. 2E and 2F depict (for illustrative purposes) how the frame ofthe device would appear if, prior to shape setting the frame, alongitudinal incision were to be made along the length of the frame at agiven circumferential location of the frame, and the frame were to thenbe laid out flat upon a surface. For some applications, withincylindrical portion 38 of the frame, the cells are cut by passing alaser along the outlines of the perimeter of the cells, as indicated bythe enlarged portion of FIG. 2E. As described hereinabove, typically,within the cylindrical portion the cells are relatively small, whichmeans that a relatively large number of cells are cut within thecircumference of the frame. Due to the size of the laser that is usedfor cutting the cells, it can be challenging passing the laser aroundthe full perimeter of the cells. However, in the vicinity of thejunctions it is desirable for the cells to be rounded, in order toreduce strain at the junctions. Therefore, for some applications, thecylindrical portion of the frame is cut as generally shown in FIG. 2F.Namely, at junctions 35, the laser cuts rounded edges 41. However,between the junctions, the laser cuts a single slit 43, rather thancutting around the perimeter of the cell.

Reference is now made to FIGS. 3A-C, which are schematic illustrationsof impeller 50 or portions thereof, in accordance with some applicationsof the present invention. Typically, the impeller includes at least oneouter helical elongate element 52, which winds around a central axialspring 54, such that the helix defined by the helical elongate elementis coaxial with the central axial spring. Typically, the impellerincludes two or more helical elongate elements (e.g., three helicalelongate elements, as shown in FIGS. 3A-C). For some applications, thehelical elongate elements and the central axial spring are made of ashape-memory material, e.g., a shape-memory alloy such as nitinol.Typically, each of the helical elongate elements and the central axialspring support a film 56 of a material (e.g., an elastomer, such aspolyurethane, and/or silicone) therebetween. For some applications, thefilm of material includes pieces of nitinol embedded therein, forexample in order to strengthen the film of material. For illustrativepurposes, the impeller is shown in the absence of the material in FIG.3A. FIGS. 3B and 3C show respective views of the impeller with thematerial supported between the helical elongate elements and the spring.

Each of the helical elongate elements, together with the film extendingfrom the helical elongate element to the spring, defines a respectiveimpeller blade, with the helical elongate elements defining the outeredges of the blades, and the axial spring defining the axis of theimpeller. Typically, the film of material extends along and coats thespring. For some applications, sutures 53 (e.g., polyester sutures,shown in FIGS. 3B and 3C) are wound around the helical elongateelements, e.g., as described in US 2016/0022890 to Schwammenthal, whichis incorporated herein by reference. Typically, the sutures areconfigured to facilitate bonding between the film of material (which istypically an elastomer, such as polyurethane, or silicone) and thehelical elongate element (which is typically a shape-memory alloy, suchas nitinol). For some applications, sutures (e.g., polyester sutures,not shown) are wound around spring 54. Typically, the sutures areconfigured to facilitate bonding between the film of material (which istypically an elastomer, such as polyurethane, or silicone) and thespring (which is typically a shape-memory alloy, such as nitinol).

Enlargements A and B of FIG. 3C show two alternative ways in which thesutures are tied around helical elongate elements 52. For someapplications, the sutures are tied around the outer surface of thehelical elongate elements, as shown in enlargement A. Alternatively, thehelical elongate elements define grooves 45 on their outer surfaces, andthe sutures are embedded within the grooves, as shown in enlargement B.By embedding the sutures within the grooves, the sutures typically donot add to the outer profile of the impeller, and the outer profile ofthe impeller is defined by the outer surfaces of the helical elongateelements.

Typically, proximal ends of spring 54 and helical elongate elements 52extend from a proximal bushing (i.e., sleeve bearing) 64 of theimpeller, such that the proximal ends of spring 54 and helical elongateelements 52 are disposed at a similar radial distance from thelongitudinal axis of the impeller, as each other. Similarly, typically,distal ends of spring 54 and helical elongate elements 52 extend from adistal bushing 58 of the impeller, such that the distal ends of spring54 and helical elongate elements 52 are disposed at a similar radialdistance from the longitudinal axis of the impeller, as each other.Typically, spring 54, as well as proximal bushing 64 and distal bushing58 of the impeller, define a lumen 62 therethrough (shown in FIG. 3C).

Reference is now made to FIG. 4, which is a schematic illustration ofimpeller 50 disposed inside frame 34 of ventricular assist device 20, inaccordance with some applications of the present invention. For someapplications, within at least a portion of frame 34, an inner lining 39lines the frame, as described hereinbelow with reference to FIGS. 19A-H.In accordance with respective applications, the inner lining partiallyoverlaps or fully overlaps with tube 24 over the portion of the framethat the inner lining lines. In the application shown in FIG. 4, theinner lining lines the inside of the cylindrical portion of the frameand tube 24 does not cover the cylindrical portion of the frame.However, the scope of the present application includes applying theapparatus and methods described with reference to FIG. 4 to any one ofthe applications described hereinbelow with reference to FIGS. 19A-H.

As shown in FIG. 4, typically there is a gap G, between the outer edgeof impeller 50 and inner lining 39, even at a location at which the spanof the impeller is at its maximum. For some applications, it isdesirable that the gap between the outer edge of the blade of theimpeller and the inner lining 39 be relatively small, in order for theimpeller to efficiently pump blood from the subject's left ventricleinto the subject's aorta. However, it is also desirable that a gapbetween the outer edge of the blade of the impeller and the innersurface of frame 34 be maintained substantially constant throughout therotation of the impeller within frame 34, for example, in order toreduce the risk of hemolysis.

For some applications, when the impeller and frame 34 are both disposedin non-radially-constrained configurations, gap G between the outer edgeof the impeller and the inner lining 39, at the location at which thespan of the impeller is at its maximum, is greater than 0.05 mm (e.g.,greater than 0.1 mm), and/or less than 1 mm (e.g., less than 0.4 mm),e.g., 0.05-1 mm, or 0.1-0.4 mm. For some applications, when the impelleris disposed in its non-radially-constrained configurations, the outerdiameter of the impeller at the location at which the outer diameter ofthe impeller is at its maximum is more than 7 mm (e.g., more than 8 mm),and/or less than10 mm (e.g., less than 9 mm), e.g., 7-10 mm, or 8-9 mm.For some applications, when frame 34 is disposed in itsnon-radially-constrained configuration, the inner diameter of frame 34(as measured from the inside of inner lining 39 on one side of the frameto the inside of inner lining on the opposite side of the frame) isgreater than 7.5 mm (e.g., greater than 8.5 mm), and/or less than 10.5mm (e.g., less than 9.5 mm), e.g., 7.5-10.5 mm, or 8.5-9.5 mm. For someapplications, when the frame is disposed in its non-radially-constrainedconfiguration, the outer diameter of frame 34 is greater than 8 mm(e.g., greater than 9 mm), and/or less than 13 mm (e.g., less than 12mm), e.g., 8-13 mm, or 9-12 mm.

Typically, an axial shaft 92 passes through the axis of impeller 50, vialumen 62 of the impeller. Further typically, the axial shaft is rigid,e.g., a rigid tube. For some applications, proximal bushing 64 of theimpeller is coupled to the shaft such that the axial position of theproximal bushing with respect to the shaft is fixed, and distal bushing58 of the impeller is slidable with respect to the shaft. The axialshaft itself is radially stabilized via a proximal radial bearing 116and a distal radial bearing 118. In turn, the axial shaft, by passingthrough lumen 62 defined by the impeller, radially stabilizes theimpeller with respect to the inner surface of frame 34, such that even arelatively small gap between the outer edge of the blade of the impellerand the inner surface of frame 34 (e.g., a gap that is as describedabove) is maintained, during rotation of the impeller.

Referring again to FIGS. 3A-C, for some applications, the impellerincludes a plurality of elongate elements 67 extending radially fromcentral axial spring 54 to outer helical elongate elements 52. Theelongate elements are typically flexible but are substantiallynon-stretchable along the axis defined by the elongate elements. Furthertypically, each of the elongate elements is configured not to exertforce upon the helical elongate element, unless force is acting upon theimpeller that is causing the helical elongate element to move radiallyoutward, such that (in the absence of the elongate element) a separationbetween the helical elongate element and the central axial spring wouldbe greater than a length of the elongate element. For example, theelongate elements may include strings (such as polyester, and/or anotherpolymer or a natural material that contains fibers) and/or wires (suchas nitinol wires, and/or wires made of a different alloy, or a metal).

For some applications, the elongate elements 67 maintain the helicalelongate element (which defines the outer edge of the impeller blade)within a given distance with respect to the central axial spring. Inthis manner, the elongate elements are configured to prevent the outeredge of the impeller from being forced radially outward due to forcesexerted upon the impeller during the rotation of the impeller. Theelongate elements are thereby configured to maintain the gap between theouter edge of the blade of the impeller and the inner surface of frame34, during rotation of the impeller. Typically, more than one (e.g.,more than two) and/or fewer than eight (e.g., fewer than four) elongateelements 67 are used in the impeller, with each of the elongate elementstypically being doubled (i.e., extending radially from central axialspring 54 to an outer helical elongate element 52, and then returningfrom the helical elongate element back to the central axial spring). Forsome applications, a plurality of elongate elements, each of whichextends from the spring to a respective helical elongate element andback to the spring, are formed from a single piece of string or a singlewire, as described in further detail hereinbelow.

For some applications, the impeller is manufactured in the followingmanner. Proximal bushing 64, distal bushing 58, and helical elongateelements 52 are cut from a tube of shape-memory material, such asnitinol. The cutting of the tube, as well as the shape setting of theshape-memory material, is typically performed such that the helicalelongate elements are defined by the shape-memory material, e.g., usinggenerally similar techniques to those described in US 2016/0022890 toSchwammenthal. Typically, spring 54 is inserted into the cut andshape-set tube, such that the spring extends along the length of thetube from at least the proximal bushing to the distal bushing. For someapplications, the spring is inserted into the cut and shape-set tubewhile the spring is in an axially compressed state, and the spring isconfigured to be held in position with respect to the tube, by exertinga radial force upon the proximal and distal bushings. Alternatively oradditionally, portions of the spring are welded to the proximal anddistal bushings. For some applications, the spring is cut from a tube ofa shape-memory material, such as nitinol. For some such applications,the spring is configured such that, when the spring is disposed in anon-radially-constrained configuration (in which the spring is typicallydisposed during operation of the impeller), there are substantially nogaps between windings of the spring and adjacent windings thereto.

For some applications, subsequent to spring 54 being inserted into thecut and shape-set tube, elongate elements 67, as described hereinabove,are placed such as to extend between the spring and one or more of thehelical elongate elements, for example, in the following manner. Amandrel (e.g., a polyether ether ketone (PEEK) and/or apolytetrafluoroethylene (PTFE) mandrel) is inserted through the lumendefined by the spring and the bushings. A string or a wire is thenthreaded such that it passes (a) from the mandrel to a first one of thehelical elongate elements, (b) back from the first of the helicalelongate elements to the mandrel, (c) around the mandrel, and to asecond one of the helical elongate elements, (d) back from the secondone of the helical elongate elements to the mandrel, etc. Once thestring or the wire has been threaded from the mandrel to each of thehelical elongate elements and back again, the ends of the string or thewire are coupled to each other, e.g., by tying them to each other. Forsome applications, sutures 53 (e.g., polyester sutures) are wound aroundthe helical elongate elements, in order to facilitate bonding betweenthe film of material (which is typically an elastomer, such aspolyurethane, or silicone) and the helical elongate elements (which istypically a shape-memory alloy, such as nitinol), in a subsequent stageof the manufacture of the impeller. For some applications, sutures(e.g., polyester sutures, not shown) are wound around spring 54.Typically, the sutures are configured to facilitate bonding between thefilm of material (which is typically an elastomer, such as polyurethane,or silicone) and the spring (which is typically a shape-memory alloy,such as nitinol), in the subsequent stage of the manufacture of theimpeller.

Typically, at this stage, a structure 59 has been assembled that is asshown in FIG. 3A. The structure includes the cut and shape-set tube thatdefines the proximal and distal bushings, the helical elongate elements,and the spring (and, optionally, the elongate elements, and thesutures). This structure is dipped into the material that defines film56. For some applications, the assembled structure is dipped into thematerial with the mandrel disposed through the lumen defined by thespring and the bushings, although it is noted that the mandrel is notshown in FIG. 3A. Typically, the material from which the film is made issilicone and/or polyurethane (and/or a similar elastomer), and theassembled structure is dipped into the material, while the material isin an uncured, liquid state. Subsequently, the material is cured suchthat it solidifies, e.g., by being left to dry. Once the material hasdried, the mandrel is typically removed from the lumen defined by thebushings and the spring.

The result of the process described above is typically that there is acontinuous film of material extending between each of the helicalelongate elements to the spring, and also extending along the length ofthe spring, such as to define a tube, with the spring embedded withinthe tube. The portions of the film that extend from each of the helicalelongate elements to the spring define the impeller blades. Forapplications in which the impeller includes elongate elements 67, theelongate elements are typically embedded within these portions of film.

Typically, impeller 50 is inserted into the left ventricletranscatheterally, while impeller 50 is in a radially-constrainedconfiguration. In the radially-constrained configuration, both helicalelongate elements 52 and central axial spring 54 become axiallyelongated, and radially constrained. Typically film 56 of the material(e.g., silicone and/or polyurethane) changes shape to conform to theshape changes of the helical elongate elements and the axial supportspring, both of which support the film of material. Typically, using aspring to support the inner edge of the film allows the film to changeshape without the film becoming broken or collapsing, due to the springproviding a large surface area to which the inner edge of the filmbonds. For some applications, using a spring to support the inner edgeof the film reduces a diameter to which the impeller can be radiallyconstrained, relative to if, for example, a rigid shaft were to be usedto support the inner edge of the film, since the diameter of the springitself can be reduced by axially elongating the spring.

As described hereinabove, for some applications, proximal bushing 64 ofimpeller 50 is coupled to axial shaft 92 such that the axial position ofthe proximal bushing with respect to the shaft is fixed, and distalbushing 58 of the impeller is slidable with respect to the shaft. Forsome applications, when the impeller is radially constrained for thepurpose of inserting the impeller into the ventricle or for the purposeof withdrawing the impeller from the subject's body, the impelleraxially elongates by the distal bushing sliding along the axial shaftdistally. Subsequent to being released inside the subject's body, theimpeller assumes its non-radially-constrained configuration (in whichthe impeller is typically disposed during operation of the impeller), asshown in FIGS. 3A-C.

It is noted that, for illustrative purposes, in some of the figures,impeller 50 is shown without including all of the features of theimpeller as shown and described with respect to FIGS. 3A-C. For example,some of the figures show the impeller not including sutures 53 and/orelongate elements 67. The scope of the present application includesusing an impeller with any of the features shown and described withrespect to FIGS. 3A-C in combination with any of the apparatus andmethods described herein.

Reference is now made to FIGS. 3D, 3E, and 3F, which are schematicillustration of impeller 50 or portions thereof, in accordance with someapplications of the present invention. As described hereinabove, forsome applications, impeller 50 includes sutures 53. Sutures 53 are woundaround the helical elongate elements 52 and are configured to facilitatebonding between the film of material (which is typically an elastomer,such as polyurethane, or silicone) and the helical elongate element(which is typically a shape-memory alloy, such as nitinol).

As an alternative or in addition to sutures 53, for some applications,coils 68 are wound around (or placed over) the helical elongateelements, as shown in FIG. 3D. For example, a tightly-wound coil (e.g.,a tightly-wound nitinol coil) may be wound around (or placed around)each of the helical elongate elements. The coil typically facilitatesbonding between the film of material and the helical elongate element byincreasing the surface area to which the material bonds at the interfacebetween the material and the helical elongate element. For someapplications, structure 59 is formed modularly (e.g., as describedhereinbelow with reference to FIG. 3F.) For some such applications, thecoils are placed around each of the elongate elements 52 (e.g., bysliding the entire coil over the elongate element in a single action),prior to the elongate elements being coupled to the proximal and distalbushings of the impeller.

As a further alternative to or in addition to sutures 53, for someapplications, sleeves 69 are placed around the helical elongateelements, as shown in FIG. 3E. For example, such sleeves may be made ofa polymer, such as polyester. The sleeves typically facilitate bondingbetween the film of material and the helical elongate elements byincreasing the surface area to which the material bonds at theinterfaces between the material and the helical elongate elements. Forsome applications, the sleeve acts as a mediator between a material fromwhich the elongate elements are made, which typically has a relativelyhigh stiffness (and is typically nitinol), and the material from whichfilm 56 is made, which is typically an elastomer having a relatively lowstiffness. The sleeve thereby enhances the strength of the couplingbetween the material and the helical elongate elements, when thematerial dries. For some applications, sleeves 69 are applied tostructure 59. For some such applications, longitudinal slits are formedin the sleeves in order to allow the sleeves to be placed around thehelical elongate elements 52. Subsequent to being placed around helicalelongate elements 52 the slits are closed (e.g., by suturing or adheringthe slits closed). For some applications, structure 59 is formedmodularly (e.g., as described hereinbelow with reference to FIG. 3F.)For some such applications, the sleeves are placed around elongateelements 52, prior to the elongate elements being coupled to theproximal and distal bushings of the impeller.

As yet a further alternative to or in addition to sutures 53, for someapplications, elongate elements 52 are shaped to have a rounded (e.g., acircular) cross section, as shown in the right portion of FIG. 3F (whichshows a cross-sectional view of an elongate element having a roundedcross-section). The left portion of FIG. 3F shows a cross-sectional viewof elongate element 52 with material of film 56 coupled to the elongateelement, in a case in which the elongate element has a non-rounded crosssection (e.g., a square or a rectangular cross section). As shown, it issometimes the case that the material (e.g., the silicone and/or thepolyurethane) from which the film is made forms a thinner layer at thecorners of an elongate element having a non-rounded cross-section. Bycontrast as shown in the left portion of FIG. 3F, when the elongateelement has a rounded cross section, the material typically forms alayer having a substantially uniform thickness at the interface with theelongate element. Therefore, for some applications, the elongateelements have rounded cross sections.

For some applications, proximal and distal bushings 64, 58 and elongateelements 52 are cut from an alloy tube, e.g., as described hereinabove.For such applications, after the tube is cut, the elongate elementstypically have non-rounded edges. Therefore for some applications,subsequent to the tube being cut, the edges of the elongate elements arerounded, for example, using grinding, sandblasting, tumble finishing,etching, plasma, surface-charging, and/or by adding rounded edges to theelongate elements. Alternatively, the proximal and distal bushings andthe elongate elements may be formed in a modular manner, and maysubsequently be coupled to each other (e.g., via welding, and/orswaging). For some such applications, the elongate elements that arecoupled to the proximal and distal bushings have rounded cross sections.As described hereinabove with reference to FIG. 3E, for someapplications, sleeves 69 are placed on the elongate elements prior tothe elongate elements being coupled to the proximal bushing and/or priorto the elongate elements being coupled to the distal bushing.

For some applications, alternative or additional techniques are used tofacilitate bonding between the film of material and the helical elongateelements. For example, the helical elongate elements may be treatedusing a surface treatment (such as, grinding, sandblasting, tumblefinishing, etching, plasma, surface-charging, etc.), in order to roughenthe outer surface of the helical elongate elements.

In accordance with the above description of FIGS. 3A-F, for someapplications of the present invention, impeller 50 is manufactured byforming a structure having first and second bushings 64, 58 at proximaland distal ends of the structure, the first and second bushings beingconnected to one another by at least one elongate element 52. The atleast one elongate element is made to radially expand and form at leastone helical elongate element, at least partially by axially compressingthe structure. An elastomeric material is coupled to the at least onehelical elongate element, such that the at least one helical elongateelement with the elastomeric material coupled thereto defines a blade ofthe impeller. Typically, the coupling is performed such that a layer ofthe material is disposed around a radially outer edge of the at leastone helical elongate element, the layer of material forming theeffective edge of the impeller blade (i.e., the edge at which theimpeller's blood-pumping functionality substantially ceases to beeffective). Further typically, the method includes performing a step toenhance bonding of the elastomeric material to the at least one helicalelongate element in a manner that does not cause a protrusion from theeffective edge of the impeller blade. For example, sutures 53 may beplaced within grooves defined by the at least one helical elongateelement, such that the sutures do not protrude from the radially outeredge of the helical elongate element, the sutures being configured toenhance bonding of the elastomeric material to the at least one helicalelongate element. Alternatively or additionally, tightly-wound coil 68may be placed around the at least one helical elongate element, suchthat the elastomeric material forms a substantially smooth layer along aradially outer edge of the coil, the coil being configured to enhancebonding of the elastomeric material to the at least one helical elongateelement. Further alternatively or additionally, sleeve 69 may be placedaround the at least one helical elongate element, such that theelastomeric material forms a substantially smooth layer along a radiallyouter edge of the sleeve, the sleeve being configured to enhance bondingof the elastomeric material to the at least one helical elongateelement. For some applications, a rounded cross section is provided tothe at least one helical elongate element, such that the elastomericmaterial forms a layer having a substantially uniform thickness at aninterface of the elastomeric material with the helical elongate element.As noted hereinabove, it is typically desirable that gap G between theouter edge of the blade of the impeller and the inner lining 39 (shownin FIG. 4) be relatively small. Therefore, it is desirable that there beno protrusion from the effective edge of the impeller blade, since thiswould occupy some of the gap between the outer edge of the impellerblade (thereby requiring a larger gap), without increasing theeffectiveness of the blood-pumping functionality of the impeller.

Reference is now made to FIGS. 3G and 3H, which are schematicillustrations of elongate elements 67 extending between each of thehelical elongate elements 52 and spring 54, in accordance with someapplications of the present invention. For some applications, arespective looped elongate element 67 extends between each of thehelical elongate elements and the spring. Typically, the looped elongateelements are closed loops that have predefined lengths and are(substantially) non-stretchable. The lengths of the looped elongateelements are typically predefined, such as to maintain the helicalelongate element (which defines the outer edge of the impeller blade)within a given distance with respect to the central axial spring, and tothereby maintain the gap between the outer edge of the blade of theimpeller and the inner surface of frame 34, during rotation of theimpeller, as described hereinabove. For some applications, the impelleris formed by looping first ends of the looped elongate elements aroundeach of the helical elongate elements as indicated in the enlargedportions of FIG. 3G and 3H. Subsequently, spring 54 is inserted throughproximal and distal bushings 64, 58, and through second ends of thelooped helical elongate elements.

For some applications, at a longitudinally-central location of spring54, the spring is shaped to define a tube 70 (i.e., without windings),as shown in FIGS. 3G and 3H. Typically, the second ends of the loopedelongate elements loop around the tube at the longitudinally-centrallocation of the spring. Typically, this reduces a risk of the loopedelongate elements tearing, relative to if the second ends of the loopedelongate elements were to loop around windings of the spring. For someapplications (not shown), the tube defines a groove therein and thesecond ends of the looped elongate elements are configured to be heldwithin the groove.

For some applications, the looped elongate element is looped around thebody of the helical elongate element, as shown in the enlarged portionsof FIG. 3G. Enlargements A and B of FIGS. 3G show two alternative waysin which the looped elongate element is looped around the body of thehelical elongate element. For some applications, looped elongate elementis looped around the outer surface of the helical elongate element, asshown in enlargement A. Alternatively, the helical elongate elementsdefine grooves 45 on their outer surfaces, and the looped elongateelement is looped around a groove 45 (such as to become embedded withinthe groove), as shown in enlargement B. By embedding the looped elongateelement within the grooves, the looped elongate element typically doesnot add to the outer profile of the impeller, and the outer profile ofthe impeller is defined by the outer surfaces of the helical elongateelements.

For some applications, the helical elongate element is shaped to definetwo holes 71 disposed in close proximity to each other, and the loopedelongate element may be looped through the holes, as shown in theenlarged portions of FIG. 3H. Enlargements A and B of FIG. 3H show twoalternative ways in which the looped elongate element is looped throughholes 71. For some applications, the looped elongate element is loopedaround the outer surface of the helical elongate element and throughholes 71, as shown in enlargement A. Alternatively, the helical elongateelements define grooves 45 on their outer surfaces, and the loopedelongate element is looped around groove 45 and through holes 71 (suchas to become embedded within the groove), as shown in enlargement B. Byembedding the looped elongate element within the grooves, the loopedelongate element typically does not add to the outer profile of theimpeller, and the outer profile of the impeller is defined by the outersurfaces of the helical elongate elements.

Referring now to FIGS. 31, 3J, and 3K, for some applications, structure59 is configured to provide a relatively long effective maximum-spanlength EML, the effective maximum-span length EML being defined as theaxial length along which the span of the impeller is at its maximum.Typically, increasing the effective maximum-span length EML of theimpeller increases the efficiency of the impeller (i.e., the amount offlow generated by the impeller at a given rotation rate). For someapplications, the angle rho that the leading edge of the impeller blademakes with respect to the longitudinal axis of the impeller is greaterthan 45 degrees, e.g., between 45 degrees and 70 degrees. As may beobserved by comparing FIG. 3J to FIG. 3I, ceteris paribus, increasingangle rho increases the effective maximum-span length EML, even if theoverall length of the impeller is not increased. Alternatively, theeffective maximum-span length EML of the impeller is increased by makingthe impeller longer, as shown in FIG. 3K.

Reference is now made to FIGS. 5A and 5B, which are schematicillustrations of impeller 50 and frame 34 of ventricular assist device20, respectively in non-radially-constrained and radially-constrainedstates thereof, in accordance with some applications of the presentinvention. The impeller and the frame are typically disposed in theradially-constrained states during the transcatheteral insertion of theimpeller and the frame into the subject's body, and are disposed in thenon-radially-constrained states during operation of the impeller insidethe subject's left ventricle. As described hereinabove, typically tube24 is disposed over at least some of the frame and extends proximallytherefrom. However, for illustrative purposes, the frame and theimpeller are shown in the absence of tube 24 in FIGS. 5A-B.

As indicated in FIG. 5B, the frame and the impeller are typicallymaintained in radially-constrained configurations by delivery catheter143. Typically, in the radially-constrained configuration of theimpeller the impeller has a total length of more than 15 mm (e.g., morethan 20 mm), and/or less than 30 mm (e.g., less than 25 mm), e.g., 15-30mm, or 20-25 mm. Further typically, in the non-radially constrainedconfiguration of the impeller, the impeller has a length of more than 8mm (e.g., more than 10 mm), and/or less than 18 mm (e.g., less than 15mm), e.g., 8-18 mm, or 10-15 mm. Still further typically, when theimpeller and frame 34 are disposed in radially constrainedconfigurations (as shown in FIG. 5B), the impeller has an outer diameterof less than 2 mm (e.g., less than 1.6 mm) and the frame has an outerdiameter of less than 2.5 mm (e.g., less than 2.1 mm).

Reference is also made to FIG. 5C, which shows a typical bearingassembly that is used in prior art axial impeller-based blood pumps.FIG. 5C is shown for the purpose of acting as a point of reference forsome of the applications of the invention described herein. As shown inFIG. 5C, a bearing assembly typically includes a radial bearing(indicated by ellipse 200) and a thrust bearing (indicated by circle202). The radial bearing is configured to reduce radial motion of theimpeller, by maintaining the axis of the impeller at a given radialposition. In response to an impeller pumping blood in a first direction,forces acting upon the impeller typically push the impeller to move inthe opposite direction to the first direction. The purpose of a thrustbearing is to oppose such motion of the impeller and to maintain theaxial position of the impeller. In the example shown in FIG. 5C, inresponse to the impeller pumping blood in the direction of arrow 204,the impeller gets pushed in the direction of arrow 206, and the thrustbearing opposes this motion. Typically, due to the frictional forcesthat are exerted upon them, bearings undergo a substantial amount ofheating and wear. Thrust bearings are typically exposed to substantialheating and wear, due to the fact that the frictional forces that areexerted upon them are typically spread over opposing surfaces having asmaller contact area between them, than is the case for radial bearings.

As described hereinabove, typically, axial shaft 92 passes through theaxis of impeller 50, via lumen 62 of the impeller. Typically, proximalbushing 64 of the impeller is coupled to the shaft via a couplingelement 65 such that the axial position of the proximal bushing withrespect to the shaft is fixed, and distal bushing 58 of the impeller isslidable with respect to the shaft. The axial shaft itself is radiallystabilized via a proximal radial bearing 116 and a distal radial bearing118.

Typically, coupling portion 31 of frame 34 is coupled to proximal radialbearing 116, for example, via snap-fit coupling, and/or via welding.Typically, at the distal end of frame 34 distal strut junctions 33 areplaced into grooves defined by the outer surface of distal radialbearing 118, the grooves being shaped to conform with the shapes of thedistal strut portions. The proximal end of distal-tip element 107 (whichdefines distal-tip portion 120) typically holds the distal strutportions in their closed configurations around the outside of distalradial bearing 118, as shown. For some applications, the device includesa distal extension 121 that extends distally from the distal radialbearing. Typically, the extension is configured to stiffen a region ofthe distal-tip element into which the distal end of shaft 92 moves(e.g., an axial-shaft-receiving tube 126, described hereinbelow, or aportion thereof).

As described above, axial shaft 92 is radially stabilized via proximalradial bearing 116 and distal radial bearing 118. In turn, the axialshaft, by passing through lumen 62 defined by the impeller, radiallystabilizes the impeller with respect to the inner surface of frame 34,such that even a relatively small gap between the outer edge of theblade of the impeller and the inner surface of frame 34 (e.g., a gapthat is as described above) is maintained, during rotation of theimpeller, as described hereinabove. For some applications, axial shaft92 is made of stainless steel, and proximal bearing 116 and/or distalbearing 118 are made of hardened steel. Typically, when crimping (i.e.,radially constraining) the impeller and the frame for the purpose ofinserting the impeller and the frame into the subject's body, distalbushing 58 of the impeller is configured to slide along the axial shaftin the distal direction, such that the impeller becomes axiallyelongated, while the proximal bushing remains in an axially fixedposition with respect to the axial shaft. More generally, the impellerchanges from its radially-constrained configuration to itsnon-radially-constrained configuration, and vice versa, by the distalbushing sliding over the axial shaft, while the proximal bushing remainsin an axially fixed position with respect to the axial shaft. (For someapplications, distal bushing 58 of the impeller is coupled to the shaftvia coupling element 65 such that the axial position of the distalbushing with respect to the shaft is fixed, and proximal bushing 64 ofthe impeller is slidable with respect to the shaft. Such applicationsare described hereinbelow with reference to FIGS. 11A-C.)

Typically, the impeller itself is not directly disposed within anyradial bearings or thrust bearings. Rather, bearings 116 and 118 act asradial bearings with respect to the axial shaft. Typically, pump portion27 (and more generally ventricular assist device 20) does not includeany thrust bearing that is configured to be disposed within thesubject's body and that is configured to oppose thrust generated by therotation of the impeller. For some applications, one or more thrustbearings are disposed outside the subject's body (e.g., within motorunit 23, shown in FIGS. 1A, 7, and 8A-B), and opposition to thrustgenerated by the rotation of the impeller is provided solely by the oneor more thrust bearings disposed outside the subject's body. For someapplications, a mechanical element and/or a magnetic element isconfigured to maintain the impeller within a given range of axialpositions. For example, a magnet (e.g., magnet 82, described hereinbelowwith reference to FIG. 7) that is disposed at the proximal end of thedrive cable (e.g., outside the subject's body) may be configured toimpart axial motion to the impeller, and/or to maintain the impellerwithin a given range of axial positions.

Reference is now made to FIGS. 6A and 6B, which are schematicillustrations of ventricular assist device 20 at respective stages of amotion cycle of impeller 50 of the ventricular assist device withrespect to frame 34 of the ventricular assist device, in accordance withsome applications of the present invention. For some applications, whilethe impeller is pumping blood through tube 24 by rotating, axial shaft92 (to which the impeller is fixated) is driven to move the impelleraxially back-and-forth within frame 34, by the axial shaft moving in anaxial back-and-forth motion, as described in further detail hereinbelowwith reference to FIG. 7. Alternatively or additionally, the impellerand the axial shaft are configured to move axially back-and-forth withinframe 34 in response to forces that are acting upon the impeller, andwithout requiring the axial shaft to be actively driven to move in theaxial back-and-forth motion. Typically, over the course of the subject'scardiac cycle, the pressure difference between the left ventricle andthe aorta varies from being approximately zero during ventricularsystole (hereinafter “systole”) to a relatively large pressuredifference (e.g., 50-70 mmHg) during ventricular diastole (hereinafter“diastole”). For some applications, due to the increased pressuredifference that the impeller is pumping against during diastole (and dueto the fact that drive cable 130 is stretchable), the impeller is pusheddistally with respect to frame 34 during diastole, relative to thelocation of the impeller with respect to frame 34 during systole. Inturn, since the impeller is connected to the axial shaft, the axialshaft is moved forward. During systole, the impeller (and, in turn, theaxial shaft) move back to their systolic positions. In this manner, theaxial back-and-forth motion of the impeller and the axial shaft isgenerated in a passive manner, i.e., without requiring active driving ofthe axial shaft and the impeller, in order to cause them to undergo thismotion. This passive axial back-and-forth motion of the impeller isdescribed in further detail hereinbelow, for example, with reference toFIG. 9. FIG. 6A shows the impeller and axial shaft disposed at theirtypical systolic positions and FIG. 6B shows the impeller and axialshaft disposed at their typical diastolic positions.

For some applications, by moving in the axial back-and-forth motion, theportions of the axial shaft that are in contact with proximal bearing116 and distal bearing 118 are constantly changing. For some suchapplications, in this manner, the frictional force that is exerted uponthe axial shaft by the bearings is spread over a larger area of theaxial shaft than if the axial shaft were not to move relative to thebearings, thereby reducing wear upon the axial shaft, ceteris paribus.Alternatively or additionally, by moving in the back-and-forth motionwith respect to the bearing, the axial shaft cleans the interfacebetween the axial shaft and the bearings from any residues, such asblood residues.

For some applications, when frame 34 and impeller 50 are innon-radially-constrained configurations thereof (e.g., when the frameand the impeller are deployed within the left ventricle), the length ofthe frame exceeds the length of the impeller by at least 2 mm (e.g., atleast 4 mm, or at least 8 mm). Typically, the proximal bearing 116 anddistal bearing 118 are each 2-4 mm (e.g., 2-3 mm) in length. Furthertypically, the impeller and the axial shaft are configured to moveaxially within the frame in the back-and-forth motion at least along thelength of each of the proximal and distal bearings, or at least alongtwice the length of each of the bearings. Thus, during theback-and-forth axial movement of the axial shaft, the axial shaft iswiped clean on either side of each of the bearings.

For some applications, the range of the impeller motion is as indicatedin FIGS. 6A-B, with 6A indicating the proximal-most disposition of theimpeller over the course of the cardiac cycle (at which the impeller istypically disposed during systole) and FIG. 6B indicating thedistal-most disposition of the impeller over the course of the cardiaccycle (at which the impeller is typically disposed during diastole). Asshown in FIG. 6A, for some applications, at its proximal-most positionthe proximal end of the impeller is disposed at location Ip, which iswithin the proximal conical section of frame 34. As shown in FIG. 6B,for some applications, at its distal-most position the distal end of theimpeller is disposed at location Id, which is at the distal end of thecylindrical section of frame 34. For the purpose of the presentapplication, the entire section of the frame from Ip to Id may beconsidered as housing the impeller, since this entire section of theframe typically houses at least a portion of the impeller over at leasta portion of the cardiac cycle. Typically, over the course of the entirecardiac cycle, the section of the impeller at which the span of theimpeller is at its maximum is disposed within the cylindrical portion ofthe frame 34. However, a proximal portion of the impeller is typicallydisposed within the proximal conical section of the frame during atleast a portion of the cardiac cycle.

Reference is again made to FIGS. 6A and 6B, and reference is also madeto FIG. 6C, which is an enlarged schematic illustration of distal-tipelement 107, which includes axial-shaft-receiving tube 126 anddistal-tip portion 120 of ventricular assist device 20, in accordancewith some applications of the present invention. Typically, distal-tipelement 107 is a single integrated element that includes bothaxial-shaft-receiving tube 126 and distal-tip portion 120. For someapplications, distal-tip element 107 is configured to be soft, such thatthe distal-tip portion is configured not to injure tissue of thesubject, even if the distal-tip portion comes into contact with thetissue (e.g., tissue of the left ventricle). For example, distal-tipelement 107 may be made of silicone, polyethylene terephthalate (PET)and/or polyether block amide (e.g., PEBAX®). For some applications, thedistal-tip portion defines a lumen 122 therethrough. For some suchapplications, during insertion of the ventricular assist device into theleft ventricle, guidewire 10 (FIG. 1B) is first inserted into the leftventricle, for example, in accordance with known techniques. Thedistal-tip portion of the ventricular assist device is then guided tothe left ventricle by advancing the distal-tip portion over theguidewire, with the guidewire disposed inside lumen 122. For someapplications, a duckbill valve 390 (or a different type of hemostasisvalve) is disposed at the distal end of lumen 122 of distal-tip portion120, as described in further detail hereinbelow.

Typically, during the insertion of the ventricular assist device intothe subject's ventricle, delivery catheter 143 is placed over impeller50 and frame 34 and maintains the impeller and the frame in theirradially-constrained configurations. For some applications, distal-tipelement 107 extends distally from the delivery catheter during theinsertion of the delivery catheter into the subject's ventricle. Forsome applications, at the proximal end of the distal-tip element, thedistal-tip element has a flared portion 124 that acts as a stopper andprevents the delivery catheter from advancing beyond the flared portion.

It is noted that the external shape of distal-tip portion in FIGS. 6A-C(as well as in some other figures) is shown as defining a complete loop,with the distal end of the distal-tip portion (within which duckbillvalve 390 is disposed) crossing over a more proximal portion of thedistal-tip portion. Typically, as a result of having had a guidewireinserted therethrough (during insertion of the ventricular assist deviceinto the left ventricle), the distal-tip portion remains partiallystraightened, even after the removal of the guidewire from thedistal-tip portion. Typically, the partial straightening of thedistal-tip portion is such that, when the distal-tip portion is disposedwithin the left ventricle, in the absence of external forces acting uponthe distal-tip portion, the distal-tip portion does not define acomplete loop, e.g., as shown in FIG. 1B, and in FIG. 23A. Other aspectsof the shape of the distal-tip portion are described in further detailhereinbelow.

Referring again to FIG. 6C, for some applications, axial-shaft-receivingtube 126 extends proximally from distal-tip portion 120 of distal-tipelement 107. As described hereinabove, typically, the axial shaftundergoes axial back-and-forth motion during the operation of impeller50. Axial-shaft-receiving tube 126 defines lumen 127, which isconfigured to receive the axial shaft when the axial shaft extendsbeyond distal bearing 118. For some applications, the shaft-receivingtube defines a stopper 128 at its distal end, the stopper beingconfigured to prevent advancement of the axial shaft beyond the stopper.For some applications, the stopper comprises a rigid component that isinserted (e.g., embedded) into the distal end of the shaft-receivingtube. Alternatively, the stopper comprises a shoulder between lumen 127of the axial-shaft-receiving tube and lumen 122 of distal-tip portion120. Typically, such a shoulder is present since lumen 122 of tipportion 120 is narrower than lumen 127. This is because lumen 127 istypically configured to accommodate the axial shaft, while lumen 122 isconfigured to accommodate guidewire 10, and the axial shaft is typicallywider than guidewire 10, since the axial shaft is itself configured toaccommodate guidewire 10 within internal lumen 132 (shown in FIGS. 10Band 10C) of the axial shaft.

Typically, during normal operation of the impeller, the axial shaft doesnot extend to stopper 128, even when drive cable 130 (shown in FIG. 7)is maximally elongated (e.g., during diastole). However, stopper 128 isconfigured to prevent the axial shaft from protruding into the tipportion when the delivery catheter is advanced over impeller 50 andframe 34, during retraction of ventricular assist device 20 from thesubject's ventricle. In some cases, during the advancement of thedelivery catheter over the frame and the impeller, the drive cable is atrisk of snapping. In the absence of stopper 128, in such cases the axialshaft may protrude into the tip portion. Stopper 128 prevents this fromhappening, even in the event that the drive cable snaps.

Typically, during operation of the ventricular assist device, andthroughout the axial back-and-forth motion cycle of the impeller, theimpeller is disposed in relatively close proximity to the distal-tipportion. For example, the distance of the impeller to the distal-tipportion may be within the distal-most 50 percent, e.g., the distal-most30 percent (or the distal-most 20 percent) of tube 24, throughout theback-and-forth motion axial cycle of the impeller.

Reference is now made to FIG. 6D, which is a schematic illustration ofimpeller 50 and axial shaft 92 of ventricular assist device 20, a regionof the axial shaft being coated with a coating or a covering material95, in accordance with some applications of the present invention. Asdescribed hereinabove, typically, distal bushing 58 of the impeller isnot fixedly coupled to the shaft. Also as described hereinabove, inorder to reduce hemolysis, it is typically desirable to maintain aconstant gap between the edges of the impeller blades and tube 24(and/or inner lining 39). Therefore, it is typically desirable to reducevibration of the impeller. For some applications, the impeller isstabilized with respect to the frame by a region along the axial shaftover which the distal bushing is configured to be slidable with respectto the axial shaft being coated such as to substantially prevent theimpeller from vibrating, by reducing a gap (e.g., by substantiallyfilling the gap) between the at least one bushing and the impeller. Forexample, the region of the axial shaft may be coated inpolytetrafluoroethylene (e.g., Teflon®) and/or diamond-like-carbon (DLC)coating or may be covered with a sleeve (which is typically a polymer,such as polyester). By substantially filling the gap between the betweenthe inner surface of distal bushing 58 and the outer surface of axialshaft 92, vibration of the impeller is typically reduced relative to ifthe region of the axial shaft were not coated. For some applications,the gap between the distal bushing and the axial shaft is less than 40micrometers, e.g., less than 30 micrometers, whether or not the axialshaft is coated. For some applications, the proximal bushing of theimpeller is configured to be slidable with respect to the axial shaft(for example, as described with reference to FIGS. 11A-C), and similartechniques to those described above are applied to the proximal bushing.

Reference is now made to FIG. 6E, which is a schematic illustration ofimpeller 50 and axial shaft 92 of ventricular assist device 20, distalbushing 58 of the impeller including a protrusion 96 from its innersurface that is configured to slide within a slot 97 defined by an outersurface of the axial shaft, in accordance with some applications of thepresent invention. As described hereinabove, typically, distal bushing58 of the impeller is not fixedly coupled to the shaft. For someapplications, protrusion 96 and slot 97 are configured to prevent thedistal end of the impeller rotating with respect to the axial shaft, asthe impeller undergoes axial motion with respect to the axial shaft.Typically, at its proximal end, slot 97 defines a stopper 98. Thestopper is configured to prevent the distal bushing from slidingproximally beyond the stopper, by preventing axial motion of protrusion96 proximally beyond the stopper. Typically, by preventing the distalbushing from sliding proximally beyond the stopper, a minimum length ofthe impeller is maintained. In turn, this typically prevents the span ofthe impeller from increasing beyond a given maximum span, whichmaintains the gap between the edges of the impeller blades and tube 24(and/or inner lining 39).

In accordance with the above description of FIGS. 6A-E (as well as thedescription of additional figures), the scope of the present inventionincludes one or more techniques for reducing hemolysis that is caused bythe pumping of blood by the impeller. Typically, frame 34, which isdisposed around the impeller defines a plurality of cells, and the frameis configured such that, in a non-radially-constrained configuration ofthe frame, the frame comprises generally cylindrical portion 38. Furthertypically, a cell width CW of each of the cells within the cylindricalportion as measured around a circumference of the cylindrical portionbeing less than 2 mm (e.g., 1.4-1.6 mm, or 1.6-1.8 mm). For someapplications, inner lining 39 lines at least the cylindrical portion ofthe frame, and the impeller is disposed inside the frame such that, in anon-radially-constrained configuration of the impeller, at a location atwhich a span of the impeller is at its maximum, the impeller is disposedwithin the cylindrical portion of the frame, such that gap G between anouter edge of the impeller and the inner lining is less than 1 mm (e.g.,less than 0.4 mm). Typically, the impeller is configured to rotate suchas to pump blood from the left ventricle to the aorta, and to bestabilized with respect to the frame, such that, during rotation of theimpeller, the gap between the outer edge of the impeller and the innerlining is maintained and is substantially constant. Typically, theimpeller is configured to reduce a risk of hemolysis by being stabilizedwith respect to the frame (such that, during rotation of the impeller,the gap between the outer edge of the impeller and the inner lining ismaintained and is substantially constant), relative to if the impellerwere not stabilized with respect to the frame.

For some applications, proximal and distal radial bearings 116 and 118are disposed, respectively, at proximal and distal ends of the frame,and axial shaft 92 passes through the proximal and distal radialbearings. Typically, the impeller is stabilized with respect to theframe by the impeller being held in a radially-fixed position withrespect to the axial shaft and the axial shaft being rigid. For someapplications, a gap between each of the axial bearings and the axialshaft is less than 15 micrometers, e.g., between 2 micrometers and 13micrometers. For some applications, the impeller includes bushings 64,58 that are disposed around the axial shaft, and at least one of thebushings (e.g., distal bushing 58) is configured to be slidable withrespect to the axial shaft. For some applications, the impeller isstabilized with respect to the frame by a region along the axial shaftover which the at least one bushing is configured to be slidable withrespect to the axial shaft being coated such as to substantially preventthe impeller from vibrating, by reducing a gap between the at least onebushing and the impeller. For example, the region may be coated in adiamond-like-carbon coating, a polytetrafluoroethylene coating, and/or apolymeric sleeve. For some applications, the gap between the distalbushing and the axial shaft is less than 40 micrometers, e.g., less than30 micrometers, whether or not the axial shaft is coated.

Reference is now made to FIGS. 6F and 6G, which are schematicillustrations of ventricular assist device 20, cylindrical portion 38 offrame 34 tapering from a proximal end of the cylindrical portion to adistal end of the cylindrical portion, in accordance with someapplications of the present invention. As described hereinabove, forsome applications, impeller 50 and axial shaft 92 are configured to moveaxially back-and-forth within frame 34 in response to forces that areacting upon the impeller, and without requiring the axial shaft to beactively driven to move in the axial back-and-forth motion. Typically,over the course of the subject's cardiac cycle, the pressure differencebetween the left ventricle and the aorta varies from being approximatelyzero during systole to a relatively large pressure difference (e.g.,50-70 mmHg) during diastole. For some applications, due to the increasedpressure difference that the impeller is pumping against during diastole(and due to drive cable 130 being stretchable), the impeller is pusheddistally with respect to frame 34 during diastole, relative to thelocation of the impeller with respect to frame 34 during systole. Inturn, since the impeller is connected to the axial shaft, the axialshaft is moved forward. During systole, the impeller (and, in turn, theaxial shaft) move back to their systolic positions. In this manner, theaxial back-and-forth motion of the impeller and the axial shaft isgenerated in a passive manner, i.e., without requiring active driving ofthe axial shaft and the impeller, in order to cause them to undergo thismotion. FIG. 6F shows the impeller disposed at its typical systolicposition and FIG. 6G shows the impeller disposed at its typicaldiastolic position.

For some applications, by virtue of the cylindrical portion of frame 34being tapered from the proximal end to the distal end of the cylindricalportion, the gap between the edges of the impeller blades and tube 24(and/or inner lining 39) is less during diastole than during systole.Due to the smaller gap between the edges of the impeller blades and tube24 (and/or inner lining 39), the pumping efficiency of the impeller istypically greater during diastole than during systole. For someapplications, it is desirable for the pumping efficiency to be greaterduring diastole than during systole, since the impeller is pumpingagainst an increased pressure gradient during diastole versus duringsystole, as described above.

Notwithstanding the description of the FIGS. 6E and 6F, it is typicallythe case that throughout the axial motion cycle of the impeller the gapbetween the edges of the impeller blades and tube 24 (and/or innerlining 39) is constant.

Reference is now made to FIG. 7, which is a schematic illustration of anexploded view of motor unit 23 of ventricular assist device 20, inaccordance with some applications of the present invention. For someapplications, computer processor 25 of control console 21 (FIG. 1A) thatcontrols the rotation of impeller 50 is also configured to control theback-and-forth motion of the axial shaft. Typically, both types ofmotion are generated using motor unit 23. The scope of the presentinvention includes controlling the back-and-forth motion at anyfrequency. For some applications, an indication of the subject's cardiaccycle is detected (e.g., by detecting the subject's ECG), and theback-and-forth motion of the axial shaft is synchronized to thesubject's cardiac cycle.

Typically, motor unit 23 includes a motor 74 that is configured toimpart rotational motion to impeller 50, via drive cable 130. Asdescribed in further detail hereinbelow, typically, the motor ismagnetically coupled to the drive cable. For some applications, an axialmotion driver 76 is configured to drive the motor to move in an axialback-and-forth motion, as indicated by double-headed arrow 79.Typically, by virtue of the magnetic coupling of the motor to the drivecable, the motor imparts the back-and-forth motion to the drive cable,which it turn imparts this motion to the impeller. As describedhereinabove and hereinbelow, for some applications, the drive cable, theimpeller, and/or the axial shaft undergo axial back-and-forth motion ina passive manner, e.g., due to cyclical changes in the pressure gradientagainst which the impeller is pumping blood. Typically, for suchapplications, motor unit 23 does not include axial motion driver 76.

For some applications, the magnetic coupling of the motor to the drivecable is as shown in FIG. 7. As shown in FIG. 7, a set of drivingmagnets 77 are coupled to the motor via a driving magnet housing 78. Forsome applications, the driving magnet housing includes ring 81 (e.g., asteel ring), and the driving magnets are adhered to an inner surface ofthe ring. For some applications a spacer 85 is adhered to the innersurface of ring 81, between the two driving magnets, as shown. A drivenmagnet 82 is disposed between the driving magnets such that there isaxial overlap between the driving magnets and the driven magnet. Thedriven magnet is coupled to a pin 131, which extends to beyond thedistal end of driven magnet 82, where the pin is coupled to the proximalend of drive cable 130. For example, the driven magnet may becylindrical and define a hole therethrough, and pin 131 may be adheredto an inner surface of the driven magnet that defines the hole. For someapplications, the driven magnet is cylindrical, and the magnet includesa North pole and a South pole, which are divided from each other alongthe length of the cylinder along a line 83 that bisects the cylinder, asshown. For some applications, the driven magnet is housed inside acylindrical housing 87. Typically, pin 131 defines a guidewire lumen133, which is described in further detail hereinbelow with reference toFIGS. 10B-C.

It is noted that in the application shown in FIG. 7, the driving magnetsare disposed outside the driven magnet. However, the scope of thepresent application includes reversing the configurations of the drivingmagnets and the driven magnet, mutatis mutandis. For example, theproximal end of the drive cable may be coupled to two or more drivenmagnets, which are disposed around a driving magnet, such that there isaxial overlap between the driven magnets and the driving magnet.

As described hereinabove, typically purging system 29 (shown in FIG. 1A)is used with ventricular assist device 20. Typically, motor unit 23includes an inlet port 86 and an outlet port 88, for use with thepurging system. For some applications, a purging fluid is continuouslyor periodically pumped into the ventricular assist device via inlet port86 and out of the ventricular assist device via outlet port 88.Additional aspects of the purging system are described hereinbelow.

Typically, magnet 82 and pin 131 are held in axially fixed positionswithin motor unit 23. The proximal end of the drive cable is typicallycoupled to pin 131 and is thereby held in an axially fixed position bythe pin. Typically, drive cable 130 extends from pin 131 to axial shaft92 and thereby at least partially fixes the axial position of the axialshaft, and in turn impeller 50. For some applications, the drive cableis somewhat stretchable. For example, the drive cable may be made ofcoiled wires that are stretchable. The drive cable typically allows theaxial shaft (and in turn the impeller) to assume a range of axialpositions (by the drive cable becoming more or less stretched), butlimits the axial motion of the axial shaft and the impeller to beingwithin a certain range of motion (by virtue of the proximal end of thedrive cable being held in an axially fixed position, and thestretchability of the drive cable being limited).

Reference is now made to FIGS. 8A and 8B, which are schematicillustrations of motor unit 23, in accordance with some applications ofthe present invention. In general, motor unit 23 as shown in FIGS. 8Aand 8B is similar to that shown in FIG. 7, and, unless describedotherwise, motor unit 23 as shown in FIGS. 8A and 8B contains similarcomponents to motor unit 23 as shown in FIG. 7. For some applications,the motor unit includes a heat sink 90 that is configured to dissipateheat that is generated by the motor. Alternatively or additionally, themotor unit includes ventilation ports 93 that are configured tofacilitate the dissipation of heat that is generated by the motor. Forsome applications, the motor unit includes vibration dampeners 94 and 96that are configured to dampen vibration of the motor unit that is causedby rotational motion and/or axial back-and-forth motion of components ofthe ventricular assist device.

As described hereinabove, for some applications, impeller 50 and axialshaft 92 are configured to move axially back-and-forth within frame 34in response to forces that act upon the impeller, and without requiringthe axial shaft to be actively driven to move in the axialback-and-forth motion. Typically, over the course of the subject'scardiac cycle, the pressure difference between the left ventricle andthe aorta varies from being approximately zero during systole to arelatively large pressure difference (e.g., 50-70 mmHg) during diastole.For some applications, due to the increased pressure difference that theimpeller is pumping against during diastole (and due to the drive cablebeing stretchable), the impeller is pushed distally with respect toframe 34 during diastole, relative to the location of the impeller withrespect to frame 34 during systole. In turn, since the impeller isconnected to the axial shaft, the axial shaft is moved forward. Duringsystole, the impeller (and, in turn, the axial shaft) move back to theirsystolic positions. In this manner, the axial back-and-forth motion ofthe impeller and the axial shaft is generated in a passive manner, i.e.,without requiring active driving of the axial shaft and the impeller, inorder to cause them to undergo this motion.

Reference is now made to FIG. 9, which is a graph indicating variationsin the length of a drive cable of a ventricular assist device, as apressure gradient against which the impeller of the ventricular assistdevice varies, as measured in experiments performed by inventors of thepresent application. An impeller and a drive cable as described hereinwere used to pump a glycerin-based solution through chambers, with thechambers set up to replicate the left ventricle and the aorta, and thesolution having properties (such as, density and viscosity) similar tothose of blood. The pressure gradient against which the impeller waspumping varied, due to an increasing volume of fluid being disposedwithin the chamber into which the impeller was pumping. At the sametime, movement of the drive cable was imaged and changes in the lengthof the drive cable were determined via machine-vision analysis of theimages. The graph shown in FIG. 9 indicates the changes in the length ofthe drive cable that were measured, as a function of the pressuregradient. The y-axis of the graph shown in FIG. 9 is such that 0 mmelongation represents the length of the drive cable when the impeller isat rest. It is noted that the graph starts at a pressure gradient valueof 65 mmHg, and that at this pressure the elongation is negative (atapproximately −0.25 mm), i.e., the drive cable is shortened relative tothe length of the drive cable prior to initiation of rotation of theimpeller. This is because the drive cable was configured such that, whenthe impeller first started pumping, the drive cable shortened (relativeto the length of the drive cable before the impeller was activated), dueto coils within the drive cable unwinding. As seen in the section of thecurve that is shown in FIG. 9, after the initial shortening of the drivecable that resulted from the aforementioned effect, it was then the casethat as the pressure gradient increased, the drive cable becameincreasingly elongated.

As indicated by the results shown in FIG. 9 and as describedhereinabove, it is typically the case that, in response to variations inthe pressure against which the impeller is pumping blood (e.g., thepressure difference between the left ventricle and the aorta), theimpeller moves back and forth with respect to frame 34. In turn, themovement of the impeller causes drive cable 130 to become more or lesselongated.

For some applications, during operation of the ventricular assistdevice, computer processor 25 of control console 21 (FIG. 1A) isconfigured to measure an indication of the pressure exerted upon theimpeller (which is indicative of the pressure difference between theleft ventricle and the aorta), by measuring an indication of tension indrive cable 130, and/or axial motion of the drive cable. For someapplications, based upon the measured indication, the computer processordetects events in the subject's cardiac cycle, determines the subject'sleft-ventricular pressure, and/or determines the subject's cardiacafterload. For some applications, the computer processor controls therotation of the impeller, and/or the axial back-and-forth motion of theaxial shaft in response thereto.

Referring again to FIG. 7, for some applications, ventricular assistdevice 20 includes a sensor 84. For example, the sensor may include aHall sensor that is disposed within motor unit 23, as shown in FIG. 7.For some applications, the Hall sensor measures variations in themagnetic field that is generated by one of the magnets in order tomeasure the axial motion of drive cable 130, and, in turn, to determinethe pressure against which the impeller is pumping. For example, theinner, driven magnet 82 may be axially longer than the outer, drivingmagnets 77. Due to the inner magnet being longer than the outer magnets,there are magnetic field lines that emanate from the inner magnet thatdo not pass to the outer magnets, and the magnetic flux generated bythose field lines, as measured by the Hall sensor, varies as the drivecable, and, in turn, the inner magnet moves axially. During operation,motor 74 rotates, creating an AC signal in the Hall sensor, whichtypically has a frequency of between 200 Hz and 800 Hz. Typically, asthe tension in the drive cable changes due to the subject's cardiaccycle, this gives rise to a low frequency envelope in the signalmeasured by the Hall sensor, the low frequency envelope typically havinga frequency of 0.5-2 Hz. For some applications, the computer processormeasures the low frequency envelope, and derives the subject's cardiaccycle from the measured envelope. It is noted that typically the axialmotion of the magnet is substantially less than that of the impeller,since the full range of motion of the impeller isn't transmitted alongthe length of the drive cable. However, it is typically the case thatthe axial back-and-forth motion of the impeller gives rise to ameasurable back-and-forth motion of the magnet.

For some applications, the Hall sensor measurements are initiallycalibrated, such that the change in magnetic flux per unit change inpressure against which the impeller is pumping (i.e., per unit change inthe pressure difference between the left ventricle and the aorta) isknown. It is known that, in most subjects, at systole, theleft-ventricular pressure is equal to the aortic pressure. Therefore,for some applications, the subject's aortic pressure is measured (e.g.,using techniques as described hereinbelow with reference to FIGS.16A-D), and the subject's left-ventricular pressure at a given time isthen calculated by the computer processor, based upon (a) the measuredaortic pressure, and (b) the difference between the magnetic fluxmeasured by the Hall sensor at that time, and the magnetic flux measuredby the Hall sensor during systole (when the pressure in the leftventricle is assumed to be equal to that of the aorta).

For some applications, generally similar techniques to those describedin the above paragraph are used, but rather than utilizing Hall sensormeasurements, a different parameter is measured in order to determineleft ventricular blood pressure at a given time. For example, it istypically the case that there is a relationship between the amount ofpower that is required to power the rotation of the impeller at a givenrotation rate and the pressure difference that is generated by theimpeller. (It is noted that some of the pressure difference that isgenerated by the impeller is used to overcome the pressure gradientagainst which the impeller is pumping, and some of the pressuredifference that is generated by the impeller is used to actively pumpthe blood from the left ventricle to the aorta, by generating a positivepressure difference between the left ventricle and the aorta. Moreover,the relationship between the aforementioned components typically variesover the course of the cardiac cycle.) For some applications,calibration measurements are performed, such that the relationshipbetween (a) power consumption by the motor that is required to rotatethe impeller at a given rotation rate and (b) the pressure differencethat is generated by the impeller, is known. For some applications, thesubject's aortic pressure is measured (e.g., using techniques asdescribed hereinbelow with reference to FIGS. 16A-D), and the subject'sleft-ventricular pressure at a given time is then calculated by thecomputer processor, based upon (a) the measured aortic pressure, (b) thepower consumption by the motor that is required to rotate the impellerat a given rotation rate at that time, and (c) the predeterminedrelationship between power consumption by the motor that is required torotate the impeller at a given rotation rate and the pressure differencethat is generated by the impeller. For some applications, theabove-described technique is performed while maintaining the rotationrate of the impeller at a constant rate. Alternatively or additionally,the rotation rate of the impeller is varied, and the variation of therotation rate of the impeller is accounted for in the above-describedcalculations.

Typically, tube 24 has a known cross-sectional area (when the tube is inan open state due to blood flow through the tube). For someapplications, the flow through tube 24 that is generated by the impelleris determined based on the determined pressure difference that isgenerated by the impeller, and the known cross-sectional area of thetube. For some applications, such flow calculations incorporatecalibration parameters in order to account for factors such as flowresistance that are specific to the ventricular assist device (or typeof ventricular assist device) upon which the calculations are performed.For some applications, the ventricular pressure-volume loop is derived,based upon the determined ventricular pressure.

Reference is now made to FIGS. 10A, 10B, and 10C, which are schematicillustrations of drive cable 130 of ventricular assist device 20, inaccordance with some applications of the present invention. Typically,the rotational motion of the impeller (which is imparted via the axialshaft), as well as the axial back-and-forth motion of the axial shaftdescribed hereinabove, is transmitted to the axial shaft via the drivecable, as described hereinabove. Typically, the drive cable extends frommotor unit 23 (which is typically disposed outside the subject's body)to the proximal end of axial shaft 92 (as shown in FIG. 10C, which showsthe connection between the distal end of the drive cable and theproximal end of the axial shaft). For some applications, the drive cableincludes a plurality of wires 134 (as shown in FIG. 10B) that aredisposed in a tightly-coiled configuration in order to impart sufficientstrength and flexibility to the drive cable, such that a portion of thecable is able to be maintained within the aortic arch (the portioncorresponding to arrow 145 in FIG. 10A), while the cable is rotating andmoving in the axial back-and-forth motion. The drive cable is typicallydisposed within a first outer tube 140, which is configured to remainstationary while the drive cable undergoes rotational and/or axialback-and-forth motion. The first outer tube is configured to effectivelyact as a bearing along the length of the drive cable. Typically, thefirst outer tube is made of a polymer (such as, polyether ether ketone)that is configured to be highly resistant to fatigue even under thefrictional forces that are generated by the relative motion between thedrive cable and the first outer tube. However, since such polymers aretypically relatively rigid, only a thin layer of the polymer istypically used in the first outer tube. For some applications, the firstouter tube is disposed within a second outer tube 142, which is made ofa material having greater flexibility than that of the first outer tube(e.g., nylon, and/or polyether block amide), and the thickness of thesecond outer tube is greater than that of the first outer tube.

Typically, during insertion of the impeller and the cage into the leftventricle, impeller 50 and frame 34 are maintained in aradially-constrained configuration by delivery catheter 143. Asdescribed hereinabove, in order for the impeller and the frame to assumenon-radially-constrained configurations, the delivery catheter isretracted. For some applications, as shown in FIG. 10A, the deliverycatheter remains in the subject's aorta during operation of the leftventricular device, and outer tube 142 is disposed inside the deliverycatheter. For some applications, during operation of the leftventricular device, a channel 224 is defined between delivery catheter143 and outer tube 142. (It is noted that the channel as shown in FIG.10A is not to scale, for illustrative purposes.) Channel 224 isdescribed in further detail hereinbelow. In order to retract the leftventricular device from the subject's body, the delivery catheter isadvanced over the impeller and the frame, such that the impeller and theframe assume their radially-constrained configurations. The catheter isthen withdrawn from the subject's body.

Referring to FIG. 10C (which shows a cross-sectional view of drive cable130 and axial shaft 92), typically, the axial shaft and the drive cabledefine a continuous lumen 132 therethrough. For some applications, theleft ventricular device is guided to the aorta and to the left ventricleby placing the axial shaft and the cable over guidewire 10 (describedhereinabove), such that the guidewire is disposed inside lumen 132.Typically, the guidewire is inserted through duckbill valve 390 (orother hemostasis valve) disposed at the distal end of distal tip portionof distal-tip element 107. The guidewire passes through guidewire lumen122 (of the distal-tip portion), and then passes into lumen 132 which isdefined by the axial shaft at that point. The guidewire then continuesto pass through lumen 132 all the way until the proximal end of thedrive cable. From the proximal end of the drive cable, the guidewirepasses through guidewire lumen 133 defined by pin 131, which is disposedoutside of the subject's body even after insertion of the distal end ofventricular assist device 20 into the subject's left ventricle.Typically, when the distal end of the ventricular assist device isdisposed inside the subject's left ventricle, the guidewire is retractedfrom the subject's body by pulling the guidewire out of the proximal endof guidewire lumen 133. Subsequently, the axial position of drivenmagnet 82 (within which pin 131 is disposed) is fixed such as to bedisposed between driving magnets 77, as shown in FIG. 7. For example, aportion of motor unit 23 in which the driven magnet is disposed may becoupled to a portion of the motor unit in which driving magnets 77 aredisposed using click-lock element 150 (shown in FIG. 13B).

For some applications, by using lumen 132 of the axial shaft and thecable in the above-described manner, it is not necessary to provide anadditional guidewire guide to be used during insertion ofleft-ventricular assist device 20. For some applications, the axialshaft and the cable each have outer diameters of more than 0.6 mm (e.g.,more than 0.8 mm), and/or less than 1.2 mm (e.g., less than 1 mm), e.g.,0.6-1.2 mm, or 0.8-1 mm. For some applications, the diameter of lumen132, defined by the shaft and the cable, is more than 0.3 mm (e.g., morethan 0.4 mm), and/or less than 0.7 mm (e.g., less than 0.6 mm), e.g.,0.3-0.7 mm, or 0.4-0.6 mm. For some applications, drive cable 130 has atotal length of more than 1 m (e.g., more than 1.1 m), and/or less than1.4 m (e.g., less than 1.3 m), e.g., 1-1.4 m, or 1.1-1.3 m. Typically,the diameters of guidewire lumen 122 and guidewire lumen 133 aregenerally similar to that of lumen 132.

Reference is now made to FIGS. 10D, 10E, and 10F, which are schematicillustrations of respective steps of a technique for coupling drivecable 130 to axial shaft 92 using a butt-welding overtube 160, inaccordance with some applications of the present invention. Typically,butt-welding overtube defines a window 162, and a helical groove 164.For some applications, axial shaft is inserted into a first end ofbutt-welding overtube, such that the proximal end of axial shaft 92 isvisible at a given location across window 162, e.g., at the halfwaypoint across the width of the window, as shown in the transition fromFIG. 10D to FIG. 10E. Subsequently, drive cable 130 is inserted into theother end of the butt-welding overtube, until the distal end of thedrive cable is also disposed at the given location across window 162(e.g., at the halfway point across the width of the window), and istypically touching the proximal end of the axial shaft, as shown in thetransition from FIG. 10E and 10F.

It is noted that the insertion of the axial shaft and the drive cableinto butt-welding overtube 160 may be in the reverse order to thatshown. Namely, the drive cable may be inserted first, followed by theaxial shaft. It is further noted that, for illustrative purposes, drivecable is shown as a tube in FIGS. 10D-F. However, the drive cabletypically includes a plurality of coiled wires, e.g., as shown in FIG.10B.

Typically, once both the axial shaft and the drive cable have beeninserted into butt-welding overtube 160, a plurality of welding rings166 are welded into the butt-welding overtube. Typically, one ring iswelded at the given location across window 162, e.g., at the halfwaypoint across the width of the window. Further typically, an additionalring is welded on either side of window 162, but at a location that isspaced from the ends of the butt-welding overtube. In this manner, theadditional welding rings weld the butt-welding overtube to the axialshaft and drive cable without the additional welding rings being weldeddirectly onto the outer surfaces of the axial shaft and the drive cable.For some applications, this places less strain on the welding ringsrelative to if the additional welding rings were to be welded at ends ofthe butt-welding overtube, such that the additional welding rings wereto be welded directly onto the outer surfaces of the axial shaft and thedrive cable. Typically, the welding rings are welded to a depth that issuch that the butt-welding overtube is welded to the axial shaft and thedrive cable, without reducing the diameter of guidewire lumen 132. Asshown, typically, the drive cable is inserted into the butt-weldingovertube, such that the helical groove is disposed around the drivecable. Typically, the helical groove provides flexibility to the portionof the butt-welding overtube that is disposed over drive cable 130.

For some applications, generally similar techniques to those describedfor welding the distal end of drive cable 130 to axial shaft 92, areused for welding the proximal end of the drive cable to pin 131(described hereinabove with reference to FIG. 7), mutatis mutandis. Forsome applications, the drive cable comprises portions having respectivecharacteristics (e.g., respective numbers of wires in the set of coiledwires that comprise the portions of the drive cable). For some suchapplications, generally similar techniques to those described forwelding the distal end of drive cable 130 to axial shaft 92, are usedfor welding the respective portions of the drive cable to each other,mutatis mutandis.

For some applications, certain features of butt-welding overtube 160 andthe techniques for use therewith are practiced in the absence of othersof the features. For example, the butt-welding overtube may include thewindow, and the welding rings may be welded in the above-describedmanner, even in the absence of the helical groove.

Reference is now made to FIGS. 11A and 11B, which are schematicillustrations of impeller 50, the impeller being coupled to axial shaft92 at the distal end of the impeller and not being coupled to the axialshaft at the proximal end of the impeller, in accordance with someapplications of the present invention. As described hereinabove,typically, axial shaft 92 passes through the axis of impeller 50, vialumen 62 of the impeller. For some applications, distal bushing 58 ofthe impeller is coupled to the shaft via coupling element 65 such thatthe axial position of the distal bushing with respect to the axial shaftis fixed, and proximal bushing 64 of the impeller is slidable withrespect to the axial shaft. The axial shaft itself is radiallystabilized via proximal radial bearing 116 and distal radial bearing118. Proximal and distal ends of frame 34 are rigidly coupled to theproximal and distal bearings, as described hereinabove. In turn, theaxial shaft, by passing through lumen 62 defined by the impeller,radially stabilizes the impeller with respect to the inner surface offrame 34, such that even a relatively small gap between the outer edgeof the blade of the impeller and the inner surface of frame 34 (e.g., agap that is as described above) is maintained, during rotation of theimpeller, as described hereinabove. For such applications, typically,when crimping (i.e., radially constraining) the impeller and the framefor the purpose of inserting the impeller and the frame into thesubject's body, proximal bushing 64 of the impeller is configured toslide along the axial shaft in the distal direction, such that theimpeller becomes axially elongated, while the distal bushing remains inan axially fixed position with respect to the axial shaft. Moregenerally, the impeller changes from its radially-constrainedconfiguration to its non-radially-constrained configuration, and viceversa, by the proximal bushing sliding over the axial shaft, while thedistal bushing remains in an axially fixed position with respect to theaxial shaft.

Reference is now made to FIG. 11C, which is a schematic illustration offirst and second coupling portions 170A and 170B for facilitating thecrimping of the impeller of FIGS. 11A-B, independently of othercomponents of frame 34, in accordance with some applications of thepresent invention. First and second portions 170A and 170B areconfigured to become engaged with each other. The first portion isdisposed on the impeller, and the second portion is coupled to frame 34and/or proximal bearing 116. Referring again to FIGS. 11A and 11B, forsome applications, prior to crimping frame 34, the impeller is radiallyconstricted, by engaging portions 170A and 170B with each other andaxially elongating the impeller, such as to radially constrict theimpeller. Subsequently, frame 34 is crimped. Typically, when theimpeller and the frame are disposed in the subject's left ventricle, thefirst and second coupling portions are decoupled from each other, suchthat the proximal end of impeller is able to move with respect to frame34 and proximal bearing 116.

Reference is now made to FIG. 12A, which is a graph showing therelationship between the pressure gradient against which the impeller ispumping and the pitch of the impeller when the impeller is configured asshown in FIGS. 11A-B. As shown, since the proximal end of the impelleris slidable, as the pressure gradient against which the impeller ispumping increases, the pitch of the impeller decreases, due to theimpeller blades being axially compressed by the pressure against whichthe impeller is pumping. Reference is also made to FIG. 12B, which is agraph showing pressure-flow curves for impellers as described hereinhaving respective pitches. Curve C1 corresponds to an impeller having arelatively small pitch, C2 corresponds to an impeller having a mediumpitch, and C3 corresponds to an impeller having a relatively largepitch. As shown, the smaller the pitch of the impeller, the greater thegradient of the pressure-flow curve, ceteris paribus. Moreover, atrelatively high pressure gradients, an impeller having a smaller pitchgenerates greater flow than an impeller having a greater pitch, whereasat relatively low pressure gradients, an impeller having a larger pitchgenerates greater flow than an impeller having a smaller pitch, ceterisparibus. In accordance with FIGS. 12A-B, for some applications, byvirtue of the impeller being coupled to the axial shaft at its distalend and being slidable with respect to the axial shaft at its proximalend, as the pressure gradient against which the impeller pumpsincreases, the pitch of the impeller decreases. Thus, at higher pressuregradients (at which a smaller pitch typically generates greater flow),the impeller has a smaller pitch, while at lower pressure gradients (atwhich a larger pitch typically generates greater flow), the impeller hasa greater pitch.

With reference to the curves shown in FIG. 12B and with respect to theimpeller as it is typically configured in the context of the presentapplication (i.e., with the proximal bearing coupled to the axial shaftand not as shown in FIGS. 11A-B), it is typically desirable that theimpeller has the following characteristics:

1) At a rotation rate of less than 20,000 RPM (e.g., less than 19,000RPM), when pumping against a pressure gradient of 100-120 mmHg, theimpeller provides positive or at least zero flow. This is so that, evenin the eventuality that there is unusually high backpressure from theaorta to the left ventricle, there is no blood flow in this direction.

2) At a rotation rate of less than 20,000 RPM (e.g., less than 19,000RPM), when pumping against a pressure gradient of more than 50 mmHg(e.g., more than 60 mmHg), for example, 50-70 mmHg, the impellerprovides flow of more than 3.5 L/min (e.g., more than 4.5 L/min), forexample 3.5-5 L/min. Under normal physiological conditions, the pressuregradient between the left ventricle and the aorta at diastole is withinthe aforementioned range, and it is desirable to provide a flow rate asdescribed even during diastole.

As indicated in the curves shown in 12B, in order to provide the firstcharacteristic an impeller having a smaller pitch (corresponding tocurve C1) is preferable, but in order to provide the secondcharacteristic an impeller having a larger pitch (corresponding to curveC3) is preferable. With this background in mind, the inventors of thepresent application have found that, in order to satisfy the first andsecond characteristics in an optimum manner, it is typically desirablefor the impeller to have a pitch that is such that, when the impeller isin its non-radially-constrained configuration, the helical elongateelements of the impeller (and therefore the impeller blades) undergo acomplete revolution of 360 degrees (or would undergo a completerevolution if they were long enough) over an axial length of more than 8mm (e.g., more than 9 mm), and/or less than 14 mm (e.g., less than 13mm), e.g., 8-14 mm, 9-13 mm, or 10-12 mm. Typically, when the impellerhas a pitch that is as described, and at a rotation rate of less than20,000 RPM (e.g., less than 19,000 RPM) the impeller provides zero orpositive flow at a pressure gradient of more than 100 mmHg, e.g., morethan 110 mmHg, and a flow of more than 3 L/min (e.g., more than 4.5L/min), for example 3.5-5 L/min, at a pressure gradient of more than 50mmHg (e.g., more than 60 mmHg), for example, 50-70 mmHg. Typically, theimpeller is configured to provide the aforementioned flow rates byvirtue of the impeller having a maximum diameter of more than 7 mm (e.g.more than 8 mm), when the impeller is in its non-radially-constrainedconfiguration.

For some applications, the pitch of helical elongate elements 52 of theimpeller (and therefore the impeller blade) varies along the lengths ofthe helical elongate elements, at least when the impeller is in anon-radially-constrained configuration. Typically, for suchapplications, the pitch increases from the distal end of the impeller(i.e., the end that is inserted further into the subject's body, andthat is placed upstream with respect to the direction of antegrade bloodflow) to the proximal end of the impeller (i.e., the end that is placeddownstream with respect to the direction of antegrade blood flow), suchthat the pitch increases in the direction of the blood flow. Typically,the blood flow velocity increases along the impeller, along thedirection of blood flow. Therefore, the pitch is increased along thedirection of the blood flow, such as to further accelerate the blood.

Reference is now made to FIG. 13A, 13B, and 13C, which are schematicillustrations of a procedure for purging drive cable 130 of ventricularassist device 20, in accordance with some applications of the presentinvention. For some applications, proximal to proximal bearing 116,axial shaft 92 and cable 130 are surrounded by first and second outertubes 140 and 142, as described hereinabove. Typically, both the firstand second outer tubes remain stationary, during rotation of the drivecable. For some applications, purging system 29 (shown in FIG. 1A)controls the flow of a purging fluid (e.g., a fluid containing glucoseor dextrose) via inlet port 86 and outlet port 88 (shown in FIGS. 7, 8A,8B, 13B, and 13C). The fluid is configured to remove air from the spacebetween the drive cable and the outer tube, and/or to reduce frictionalforces between drive cable 130 (which rotates), and outer tube 140(which remains stationary, during rotation of the drive cable), and/orto reduce frictional forces between axial shaft 92 and proximal bearing116 and/or distal bearing 118.

Referring to FIG. 13A, for some applications, the purging fluid ispumped between the first and second outer tubes, and there is an opening146 within the first outer tube in the vicinity of the proximal bearing.For some applications, the purging fluid flows between first outer tube140 and drive cable 130 via opening 146, as indicated bypurging-fluid-flow arrow 148 in FIG. 13A. In this manner, the interfacebetween drive cable 130 (which rotates), and outer tube 140 (whichremains stationary, during rotation of the drive cable) is purged. Forsome applications, some of the purging fluid additionally flows to theinterface between the axial shaft and proximal bearing 116, therebypurging the interface (and/or reducing frictional forces at theinterface), as indicated by purging-fluid-flow arrows 149 in FIG. 13A.Typically, the flow of the purging fluid in the direction of arrows 149also prevents blood from flowing into the interface between the axialshaft and the proximal bearing.

As described hereinabove (with reference to FIG. 10B) typically thedrive cable includes a plurality of coiled wire. For some applications,purging fluid passes into lumen 132 defined by the drive cable via gapsin the coiled wires. Once the purging fluid is disposed within lumen 132it flows in both proximal and distal directions, as indicated by arrow151 of FIG. 13A. The purging fluid that flows in the distal directiontypically flows out of the distal end of lumen 132 and toward lumen 122defined by distal-tip portion, as indicated by arrow 152 of FIG. 13A. Atthe end of distal-tip portion, the purging fluid is typically preventedfrom flowing out of the distal-tip portion by duckbill valve 390.Therefore, some of the purging fluid typically flows to the interfacebetween the axial shaft and distal bearing 118, thereby purging theinterface (and/or reducing frictional forces at the interface), asindicated by purging-fluid-flow arrows 154 in FIG. 13A. Typically, theflow of the purging fluid in the direction of arrows 154 also preventsblood from flowing into the interface between the axial shaft and thedistal bearing.

As described above, once the purging fluid is disposed within lumen 132it flows in both proximal and distal directions, as indicated by arrow151 of FIG. 13A. Referring now to FIG. 13B, typically, at the proximalend of ventricular assist device 20, the purging fluid flows in thedirection of arrows 156 out of the proximal end of lumen 132 and thenout of the proximal end of lumen 133 defined by pin 131. For someapplications, the purging fluid then flows in the direction of arrow 157and around driven magnet, such as to reduce frictional forces that thedriven magnet is exposed to. For some applications, the purging fluidthen flows out of outlet port 88, in the direction of arrow 158.Typically, the purging fluid is then disposed of. Alternatively, thepurging fluid is pumped back into the device, via inlet port 86.

With reference to the above description of the purging procedure that istypically used with ventricular assist device 20, it is noted thatguidewire lumens 122, 132, and 133 (which were previously used tofacilitate insertion of the device over guidewire 10, as describedhereinabove), are typically used as flow channels for purging fluid,during use of the ventricular assist device.

Referring now to FIG. 13C, for some applications, ventricular assistdevice includes an additional purging fluid inlet port 89, which istypically used to pump purging fluid into channel 224 between deliverycatheter 143 and outer tube 142. For some applications, the purgingfluid is pumped into this channel at a low enough pressure, that it isstill possible to detect aortic blood pressure via this channel, asdescribed in further detail hereinbelow. For some applications, ratherthan continuously pumping purging fluid into channel 224, fluid ispumped into this channel periodically in order to flush the channel. Forsome applications, port 89 and channel 224 are used for aortic pressuresensing, as described in further detail hereinbelow.

Reference is now made to FIG. 13D, which is a schematic illustration ofventricular assist device 20 that includes an inflatable portion 153(e.g., a balloon) on its distal tip, the inflatable portion beingconfigured to be inflated by a fluid that is used for purging the drivecable of the device, in accordance with some applications of the presentinvention. As described hereinabove, with reference to FIG. 13A, forsome applications, purging fluid is pumped through lumen 132 defined bydrive cable 130 and axial shaft 92, such that at least some fluid flowsall the way to the distal end of the axial shaft. Typically, for suchapplications, the purging fluid continues to flow into lumen 122 ofdistal-tip portion 120. For some applications, inflatable portion 153 isdisposed around the distal-tip portion, and a there is an opening 155between lumen 122 and the interior of the inflatable portion. Theinflatable portion is inflated by the purging fluid entering theinterior of the inflatable portion, via opening 155. For someapplications, by controlling the pressure at which the purging fluid ispumped into ventricular assist device 20, the inflation of theinflatable portion is controlled.

It is noted that, in accordance with some applications of the presentinvention, the shape of distal-tip element 107 as shown in FIG. 13D (aswell as in FIGS. 16A, 16B, 16E, 17D, 30, and 31, for example) isgenerally as described in US 2019/0209758 to Tuval, which isincorporated herein by reference. The scope of the present inventionincludes combining the apparatus and methods described with respect toany one of the figures with any of the shapes of the distal-tip elementdescribed herein. It is further noted that, in accordance with someapplications of the present invention, the configuration of frame 34 asshown in FIG. 13D is generally as described in US 2019/0209758 to Tuval,which is incorporated herein by reference. The scope of the presentinvention includes combining the apparatus and methods described withrespect to any one of the figures with any of the shapes of thedistal-tip portion and/or configurations of frame 34 described herein.

Referring to FIG. 13E, for some applications, as an alternative topumping a purging fluid through the ventricular assist device throughoutthe operation of the ventricular assist device, fluid 147 is initiallyreleased into the space between drive cable 130 (which rotates), andouter tube 140 (which remains stationary, during rotation of the drivecable), such that the fluid fills the space between the drive cable andouter tube 140, as well as lumen 132. The fluid is then kept in place,between the drive cable and outer tube 140, and within lumen 132,typically, throughout the operation of the ventricular assist device.The fluid is configured to remove air from the space between the drivecable and the outer tube, and/or to reduce frictional forces betweendrive cable 130 (which rotates), and outer tube 140 (which remainsstationary, during rotation of the drive cable), and/or to reducefrictional forces between axial shaft and proximal bearing 116 and/ordistal bearing 118. For some applications, the fluid is additionallyconfigured to fill the space between tube 140 and tube 142, e.g., bypassing through holes defined by tube 140. For some such applications,heat conducting elements are disposed within the first outer tube and/orthe second outer tube, in order to dissipate heat from regions at whicha large amount of heat is generated by frictional forces.

For some applications, the fluid has a relatively high viscosity, e.g. aviscosity of more than 100 mPa·s (e.g., more than 500 mPa·s), forexample, between 100 mPa·s and 1000 mPa·s, such that the fluid remainssubstantially in place, during operation of the ventricular assistdevice. For example, petroleum jelly and/or ultrasound coupling gel maybe used as the fluid. For some applications, in order to pump the fluidtoward the distal end of the ventricular assist device, the fluid isinitially heated, in order to temporarily decrease its viscosity.

Reference is now made to FIGS. 14A, 14B, and 14C, which are schematicillustrations of a stator 250 configured to be disposed inside tube 24of ventricular assist device 20, proximal to frame 34 and impeller 50,in accordance with some applications of the present invention. For someapplications, the stator is made of a frame 252 that is coupled to outertube 142, and a flexible material 254 (e.g. polyurethane, polyester,silicone, polyethylene terephthalate (PET), and/or polyether block amide(PEBAX®) that is coupled to the frame. Typically, the stator is shapedto define a plurality of curved projections 256 (e.g., more than 2,and/or less than 8 curved projections) that extend radially from outertube 142, when device 20 is in a non-radially-constrained configuration.The curvature of the curved projections is typically such as to opposethe direction of rotation of the impeller. The stator is typicallyconfigured to reduce rotational flow components from the blood flowprior to the blood flowing from outlet openings 109 of tube 24. For someapplications, the projections of stator 250 are not curved.

Typically, during the insertion of tube 24 to the left ventricle, thecurved projections of the stator are radially constrained by deliverycatheter 143. Upon being released from the delivery catheter, the curvedprojections are configured to automatically assume their curvedconfigurations.

Reference is now made to FIGS. 15A, 15B, 15C, 15D, and 15E, which areschematic illustration of a stator 260 that is defined by tube 24 ofventricular assist device 20, in accordance with some applications ofthe present invention. Typically, stator 260 defined by a portion oftube 24 that is disposed proximally with respect to frame 34 andimpeller 50, and is configured to reduce rotational flow components fromthe blood flow prior to the blood flowing from outlet openings 109 oftube 24. For some applications, stator 260 is made up of one or morecurved ribbons 262 that curve around outer tube 142 within tube 24, asshown in FIG. 15A. Alternatively or additionally, stator 260 comprises aportion 266 of tube 24, which is twisted, such that the walls of thetube itself define folds that are such as to reduce rotational flowcomponents from the blood flow prior to the blood flowing from outletopenings 109 of tube 24, as shown in FIG. 15B.

For some applications, along a portion of tube 24 between the proximalend of frame 34 and outlet openings 109, the tube is split into aplurality of compartments 267 by a plurality of curved ribbons 262, suchthat the compartments define intertwined helices along the length of theportion of the tube, as shown in FIG. 15C. Alternatively, along aportion of tube 24 between the proximal end of frame 34 and outletopenings 109, the tube is split into a plurality of compartments 269 bya plurality of ribbons 264 that are parallel with the longitudinal axisof tube 24, as shown in FIG. 15D. For some applications, within aportion of tube 24 between the proximal end of frame 34 and outletopenings 109, tube 24 includes a plurality of helical tubes 268 that areconfigured to function as stator 260. For some applications, the helicaltubes are twisted around each other, as shown. Typically, each of theexamples of stator 260 shown in FIGS. 15A, 15B, 15C, 15D, and 15E isconfigured to reduce rotational flow components from the blood flowprior to the blood flowing from outlet openings 109 of tube 24.

Reference is now made to FIGS. 16A and 16B, which are schematicillustrations of ventricular assist device 20, the ventricular assistdevice including one or more ventricular blood-pressure-measurementtubes 220, in accordance with some applications of the presentinvention. As described hereinabove, typically, the ventricular assistdevice includes tube 24, which traverses the subject's aortic valve,such that a proximal end of the tube is disposed within the subject'saorta and a distal end of the tube is disposed within the subject's leftventricle. Typically, a blood pump (which typically includes impeller50), is disposed within the subject's left ventricle within tube 24, andis configured to pump blood through tube 24 from the left ventricle intothe subject's aorta. For some applications, ventricularblood-pressure-measurement tube 220 is configured to extend to at leastan outer surface 212 of tube 24, such that an opening 214 at the distalend of the blood-pressure-measurement tube is in direct fluidcommunication with the patient's bloodstream outside tube 24. Typically,opening 214 is configured to be within the subject's left ventricleproximal to the blood pump (e.g., proximal to impeller 50). A pressuresensor 216 (illustrated schematically in FIG. 1A) measures pressure ofblood within the ventricular blood-pressure-measurement tube. Typically,by measuring pressure of blood within the left ventricularblood-pressure-measurement tube, the pressure sensor thereby measuresthe subject's blood pressure outside tube 24 (i.e., left ventricularblood pressure). Typically, blood-pressure-measurement tube 210 extendsfrom outside the subject's body to opening 214 at the distal end of thetube, and pressure sensor 216 is disposed toward a proximal end of thetube, e.g., outside the subject's body. For some applications, computerprocessor 25 (FIG. 1A), receives an indication of the measured bloodpressure and controls the pumping of blood by the impeller, in responseto the measured blood pressure.

For some applications, the ventricular assist device includes two ormore such ventricular blood-pressure-measurement tubes 220, e.g., asshown in FIGS. 16A and 16B. For some applications, based upon the bloodpressure as measured within each of the left ventricularblood-pressure-measurement tubes, computer processor 25 determineswhether the opening of one of the two or more ventricularblood-pressure-measurement tubes is occluded. This may occur, forexample, due to the opening coming into contact with the wall of theinterventricular septum, and/or a different intraventricular portion.Typically, in response to determining that the opening of one of the twoor more ventricular blood-pressure-measurement tubes is occluded, thecomputer processor determines the subject's left-ventricular pressurebased upon the blood pressure measured within a different one of the twoor more ventricular blood-pressure-measurement tubes.

Referring to FIG. 16A, as described hereinabove, for some applications,drive cable 130 extends from a motor outside the subject's body to axialshaft 92 upon which impeller 50 is disposed. Typically, the drive cableis disposed within outer tube 142. For some applications, the drivecable is disposed within first outer tube 140 and second outer tube 142,as described hereinabove. For some applications, aortic blood pressureis measured using at least one aortic blood-pressure-measurement tube222 that defines an opening 219 in outer tube 142 at its distal end. Theaortic blood-pressure-measurement tube is configured to extend fromoutside the subject's body to an outer surface of outer tube 142 withinthe subject's aorta, such that the opening at the distal end of theaortic blood-pressure-measurement tube is in direct fluid communicationwith the subject's aortic bloodstream. Blood pressure sensor 216 isconfigured to measure the subject's aortic blood pressure by measuringblood pressure within the aortic blood-pressure-measurement tube.

For some applications, the one or more ventricular blood-pressuremeasurement tubes 220 and/or one or more aortic blood-pressuremeasurement tubes 222 are disposed within outer tube 142, surroundingthe drive cable. For some applications, portions of the one or moreblood-pressure-measurement tubes are defined by the walls of outer tube142, as shown in the cross-sections of FIGS. 16A and 16B. For someapplications, within outer tube 142, the blood pressure measurementtubes have elliptical cross-sections (as shown). Typically, thisincreases the cross-sectional areas of the tubes, relative to if theywere to have circular cross-sections. Typically, within a distal portionof each of the ventricular blood-pressure measurement tubes 220 (whichextends to opening 214), the tube has a circular cross-section. For someapplications, the diameter of the distal portion of the tube is morethan 0.2 mm, and/or less than 0.5 mm (e.g., 0.2-0.5 mm).

As shown in FIGS. 16A and 16B, for some applications, outer tube 142defines a groove 215 in a portion of the outer surface of the outer tubethat is configured to be disposed within tube 24. Typically, duringinsertion of the ventricular assist device into the subject's body, theportion of ventricular blood-pressure-measurement tube 220 that extendsfrom within tube 24 to at least an outer surface of tube 24, isconfigured to be disposed within the groove, such that the portion ofthe ventricular blood-pressure-measurement tube does not protrude fromthe outer surface of the outer tube.

Reference is now made to FIGS. 16C and 16D, which are schematicillustrations of ventricular assist device 20, the device having anaortic blood pressure measurement channel 224 within delivery catheter143, in accordance with some applications of the present invention.

For some applications, during operation of the ventricular assistdevice, channel 224 is defined between delivery catheter 143 and outertube 142 that extends from the distal end of the delivery catheter tothe proximal end of the delivery catheter. For example, FIG. 10A shows agap between the outside of outer tube 142 and the inside of deliverycatheter 143, which can function as the aforementioned channel. (It isnoted that the scale of the channel as shown in FIG. 10A is not toscale, for illustrative purposes.) Typically, during operation of theventricular assist device, the distal end of the delivery catheter isdisposed within the subject's aorta, and the proximal end of thedelivery catheter is disposed outside the subject's body. Therefore, bysensing pressure within the channel between delivery catheter 143 andouter tube 142, blood pressure sensor 216 (which is shown in Fig. lA andwhich is typically disposed outside the subject's body) is able todetect aortic pressure. For some applications, the pressure sensorsenses aortic pressure via port 89, shown in FIG. 13C. As notedhereinabove, with reference to FIG. 13C, purging fluid is typicallypumped into the channel between delivery catheter 143 and outer tube142. For some applications, the purging fluid is pumped into thischannel at a low enough pressure, that it is still possible to detectaortic blood pressure via the channel, in the above-described manner.

For some applications, a spacing tube 240 is placed between outer tube142 and delivery catheter 143 along at least a distal portion ofdelivery catheter 143, such as to fill the gap between the outer tubeand the delivery catheter. For some applications, the spacing tube isconfigured to prevent debris, emboli, and/or other matter from flowingout of the distal end of the delivery catheter from where they couldflow into carotid arteries 241. For some applications, the deliverycatheter defines a lateral hole 242, which is exposed to the aorticblood stream. For some such applications, proximal of hole 242, thespacing tube is not disposed between the delivery catheter and the outertube, as shown in FIG. 16C. Thus, proximal of hole 242, channel 224 isdefined between the delivery catheter and outer tube 142, such that thesubject's aortic blood pressure is detected via channel 224, in themanner described hereinabove. Alternatively, proximal of hole 242, thespacing tube is disposed between the delivery catheter and the outertube, but the spacing tube defines channel 224 which extends from thehole to the proximal end of the delivery catheter, as shown in FIG. 16D.Typically, the subject's aortic blood pressure is detected via channel224, in the manner described hereinabove (e.g., via port 89).

Reference is now made to FIG. 16E, which is a schematic illustration ofventricular assist device 20, the device including one or moreblood-pressure-measurement sensors 270 that are disposed on an outersurface of tube 24, in accordance with some applications of the presentinvention. For some applications, generally similar techniques to thosedescribed with reference to ventricular blood-pressure-measurement tube220 are performed using an electrical wire 272 that extends alongblood-pump tube 24 (and that typically extends from outside thesubject's body) to the outer surface of tube 24.Blood-pressure-measurement sensor 270 is disposed at a tip of the wirein electrical communication with the subject's bloodstream outside oftube 24. The subject's blood pressure outside tube 24 (e.g., thesubject's ventricular blood pressure and/or the subject's aortic bloodpressure) is measured by detecting an electrical parameter using thesensor. For some applications, wire 272 and/or sensor 270 is printedonto the outer surface of tube 24.

For some applications, sensor 270 is configured to perform conductancemeasurements. For some applications, conductance sensors are disposedinside tube 24 (rather than on the outer surface of tube 24), but areconfigured to sense conductance using frequency that is substantiallynot attenuated by tube 24. For some applications, additional conductancesensors are disposed on the left-ventricular assist device, for example,on distal-tip element 107. For some such applications, computerprocessor 25 (FIG. 1A) applies a current between the most distalelectrode, which is typically configured to be disposed near the apex ofthe heart, and the most proximal electrode, which is typicallyconfigured to be disposed above the aortic valve. Conductance of thatcurrent between each pair of the electrodes is then measured by thecomputer processor. For some applications, the application of thecurrent, and the conductance measurements, are performed using generallysimilar techniques to those described in an article entitled “TheConductance Volume Catheter Technique for Measurement of LeftVentricular Volume in Young Piglets,” by Cassidy et al. (PediatricResearch, Vol. 31, No. 1, 1992, pp. 85-90). For some applications, thecomputer processor is configured to derive the subject's real-timeleft-ventricular pressure-volume loop based upon the conductancemeasurements. For some applications, the computer processor controls arate of rotation of the impeller responsively to the derivedpressure-volume loop.

For some applications, the subject's ventricular blood pressure isderived from the conductance measurements. For some such applications,the subject's aortic blood pressure is measured (e.g., as describedhereinabove). The subject's left ventricular pressure is derived bymeasuring conductance measurements over the course of the subject'scardiac cycle, and determining the difference between the leftventricular pressure and the aortic pressure at any given point withinthe cardiac cycle, based upon having previously calibrated theconductance measurements with left-ventricular/aortic pressuregradients. For some applications, the computer processor is configuredto calculate the first derivative of the left-ventricular pressuremeasurements. Typically, such changes are indicative of the rate ofchange of pressure within the left ventricle, which itself is animportant clinical parameter. It is noted that the first derivative ofthe left-ventricular pressure is typically unaffected by changes inaortic pressure, since the aortic pressure curve is relatively flat asthe left-ventricular pressure curve undergoes changes that are ofclinical importance.

Reference is now made to FIGS. 17A, 17B, 17C, and 17D, which areschematic illustrations of outer tube 142 of ventricular assist device20, the outer tube including a pitot tube 225 that is configured tomeasure blood flow through tube 24 of the device, in accordance withsome applications of the present invention. The portion of outer tube142 shown in FIGS. 17A-D is typically disposed within tube 24. For someapplications, a flow obstacle 226 (which is typically funnel shaped) isconfigured to create a stagnation region near a stagnation pressure tap227. For some applications, flow straighteners 228 are added to theouter surface of tube 142, in order remove any swirling component of theflow (which does not contribute to the axial flow rate), as shown inFIG. 17A. Alternatively, the stagnation pressure tap is disposedsufficiently proximally within funnel-shaped flow obstacle 226 that theflow obstacle itself acts to remove the swirling components of the flow,prior to the blood reaching the stagnation pressure tap, as shown inFIG. 17B. For some applications, the stagnation pressure tap includes ashort tube 233 that protrudes from outer tube 142 within funnel-shapedflow obstacle 226, such that the opening of short tube 233 faces thedirection of axial blood flow through tube 24, as shown in FIG. 17C.Outer tube 142 additionally defines opening 219, which functions as astatic pressure tap 229. The pressure within stagnation pressure tap 227and within static pressure tap 229 is measured using a pressure sensor,e.g., a pressure sensors that are disposed outside the subject's body,as described hereinabove with reference to FIGS. 16A-D.

In some applications, flow through tube 24 is calculated based upon thepressure measurements. For example, flow through tube 24 may becalculated using the following equation:

$Q = {C \cdot A \cdot \sqrt{\frac{2\Delta \; P}{\rho}}}$

in which:

Q is the flow through tube 24,

C is a calibration constant that is empirically determined and accountsfor factors such as impeller velocity and the geometries of pressuretaps 227 and 229,

A is the cross-sectional area of tube 24 (not including the area thatouter tube 142 occupies),

ΔP is the difference between the stagnation pressure (measured viapressure tap 227), and the static pressure (measured via pressure tap229)

ρ is the fluid density of blood.

Referring to FIG. 17D, for some applications a region 230 of tube 24within which pitot tube 225 is disposed is narrowed with respect to therest of the cylindrical portion of tube 24. For some applications, thenarrowing of the region facilitates more accurate measurements beingmade using the pitot tube. For some applications, narrow region 230 oftube 24 is configured to be placed within the subject's aortic valve.Typically, the narrowing of the tube at region 230 is configured tofacilitate placement of region 230 at the aortic valve. For someapplications, tube 24 includes narrow region 230 even in the absence ofpitot tube 225, in order to facilitate placement of this region of thetube at the aortic valve, in the above-described manner.

Reference is now made to FIG. 18, which is a schematic illustration ofventricular assist device 20, the ventricular assist device includingcoronary artery tubes and/or wires 304, in accordance with someapplications of the present invention. For some applications, one ormore tubes and/or wires extend along the outside or the inside of aproximal portion of tube 24. The tubes and/or wires are shape set, suchthat in non-radially-constrained configurations of the tubes and/orwires, distal ends of the tubes and/or wires extend radially from theouter surface of tube 24. The tubes and/or wires are positioned toextend radially from an axial location along tube 24 such that, when thedistal ends of the tubes and/or wires are positioned at the subject'scoronary arteries 306, pump portion 27 of the device is correctlypositioned within the subject's left ventricle 22. For someapplications, a medical professional who is deploying ventricular assistdevice 20, ensures that pump portion 27 of the device is correctlypositioned within the subject's left ventricle 22, by inserting thedistal ends of the tubes and/or wires into the coronary arteries 306.For some applications, tubes are used in the above-describedembodiments, and the tubes extend proximally to the proximal end of theventricular assist device (e.g., via outer tubes 140, 142, and/or viadelivery catheter 143). For some such applications, a procedure isperformed with respect to one or more of the coronary arteries via thetubes. Alternatively or additionally, contrast agent is injected via thetubes, in order to facilitate imaging of the current location of thedevice. For some applications, generally similar techniques areperformed using ventricular blood-pressure measurement tubes 220,described hereinabove. For example, contrast agent may be injected viathe blood-pressure measurement tubes, in order to facilitate imaging ofthe current location of the device.

Reference is now made to FIGS. 19A, 19B, 19C, 19D, 19E, 19F, 19G, and19H, which are schematic illustrations of ventricular assist device 20,the device including inner lining 39 that lines the inside of frame 34that houses impeller 50, in accordance with some applications of thepresent invention. (For illustrative purposes, inner lining 39 and tube24 on the side of the device facing out of the page are shown astransparent in FIGS. 19A-E.) For some applications, inner lining 39 isdisposed inside frame 34, in order to provide a smooth inner surfacethrough which blood is pumped by impeller. Typically, by providing asmooth surface, the covering material reduces hemolysis that is causedby the pumping of blood by the impeller, relative to if the blood werepumped between the impeller and struts of frame 34. For someapplications, inner lining includes polyurethane, polyester, and/orsilicone. Alternatively or additionally, the inner lining includespolyethylene terephthalate (PET) and/or polyether block amide (PEBAX®).

Typically, the inner lining is disposed over at least the inner surfaceof the cylindrical portion of frame 34 (the cylindrical portion beingindicated in FIGS. 2A-C, for example). For some applications, tube 24also covers the cylindrical portion 38 of frame 34, around the outsideof the frame, for example, such that tube 24 and inner lining 39 overlapover at least 50 percent of the length of the inner lining, for example,over the entire length of the cylindrical portion of frame 34, e.g., asshown in FIG. 19A. For some applications, there is only partial overlapbetween tube 24 and inner lining 39, e.g., as shown in FIG. 19B. Forexample, tube 24 may overlap with inner lining along less than 50percent (e.g., along less than 25 percent) of the length of the innerlining. For some such applications, during insertion of ventricularassist device 20 into the subject's body, the impeller is advanceddistally within frame 34, such that the impeller is not disposed withinthe area of overlap between the tube and the inner lining, such thatthere is no longitudinal location at which the impeller, tube 24, frame34, and inner lining 39 all overlap with each other.

Typically, for applications as shown in FIGS. 19A and 19B, over the areaof overlap between inner lining 39 and tube 24, the inner lining isshaped to form a smooth surface (e.g., in order to reduce hemolysis, asdescribed hereinabove), and tube 24 is shaped to conform with the strutsof frame 34 (e.g., as shown in the cross-section in FIG. 19A).Typically, over the area of overlap between inner lining 39 and tube 24,the tube and the inner lining are coupled to each other, e.g., viavacuum, via an adhesive, and/or using a thermoforming procedure, forexample as described hereinbelow.

For some applications, inner lining 39 and tube 24 are made of differentmaterials. For example, the inner lining may be made of polyurethane,and the tube may be made of polyether block amide (PEBAX®). Typically,the material from which the inner lining is made has a higherthermoforming temperature than that of the material from which the tubeis made. For some applications in which the inner lining and the tubeoverlap along at least a portion of frame 34 (e.g., along thecylindrical portion of frame 34), the tube and the inner lining arebonded to each other and/or the frame in the following manner.Initially, the inner lining is placed over a mandrel. The frame is thenplaced over the inner lining. Subsequently, tube 24 is placed around theoutside of the frame. For some applications, in order to mold tube 24 toconform with the struts of frame 34, without causing the inner lining todeform, the frame is heated to a temperature that is above thethermoforming temperature of tube 24 but below the thermoformingtemperature of inner lining 39. Typically, the frame is heated frominside the frame, using the mandrel. Typically, while the frame isheated to the aforementioned temperature, an outer tube (which istypically made from silicone) applies pressure to tube 24 that causestube 24 to be pushed radially inwardly, in order to cause the tube toconform with the shapes of the struts of the frame, as shown in thecross-section of FIG. 19A. For some applications, the combination of theframe, the inner lining, and the portion of tube 24 disposed around theframe is subsequently shape set to a desired shape and dimensions usingshape setting techniques that are known in the art.

In accordance with the above description, the scope of the presentinvention includes a method for manufacturing a housing for an impellerof a blood pump that includes performing the following steps. An innerlining is placed around a mandrel. A cylindrical portion of a frame isplaced around the inner lining, the cylindrical portion of the frameincluding struts that define a generally cylindrical shape. A distalportion of an elongate tube is placed around at least a portion of theframe, the tube including a proximal portion that defines at least oneblood outlet opening. While the distal portion is disposed around atleast the portion of the frame, the inner lining, the frame and thedistal portion of the elongate tube are heated, via the mandrel. Whileheating the inner lining, the frame and the distal portion of theelongate tube, pressure is applied from outside the distal portion ofthe elongate tube, such as to cause the distal portion of the elongatetube to conform with a structure of the struts of the frame, and such asto cause the inner lining and the distal portion of the elongate tube tobecome coupled to the frame. For example, the pressure may be applied bymeans of a silicone tube that is placed outside the distal portion ofthe elongate tube. For some applications, the inner lining and theelongate tube include an inner lining and elongate tube that are madefrom different materials from each other, and a thermoformingtemperature of a material from which the inner lining is made is higherthan a thermoforming temperature of a material from which the elongatetube is made. For some such applications, the inner lining, the frameand the distal portion of the elongate tube are heated to a temperaturethat is above the thermoforming temperature of the material from whichthe elongate tube is made and below the thermoforming temperature of thematerial from which the inner lining is made.

Referring to FIG. 19C, for some applications, tube 24 does not overlapwith inner lining 39, but tabs 322 extend through struts of frame 34from tube 24 to inner lining 39, and are used to sealingly couple thetube to the inner lining (e.g., by being adhered to the inner lining).Alternatively or additionally (not shown), tabs 322 extend from theinner lining to tube 24 and are used to sealingly couple the tube to theinner material (e.g., by being adhered to the tube).

As described hereinabove, for some applications, the combination of theframe, the inner lining, and the portion of tube 24 disposed around theframe is shape set to a desired shape and dimensions using shape settingtechniques that are known in the art. Referring to FIG. 19D, for someapplications, the combination of the frame, the inner lining, and theportion of tube 24 disposed around the frame is shape set such that adistal portion 330 of cylindrical portion 38 of the frame is widenedwith respect to the rest of the cylindrical portion of the frame.Typically, the widening of the frame is such that blood inlet opening108 (which is typically defined by the inner lining at the distal end ofthe cylindrical portion of the frame) is widened relative the rest ofthe cylindrical portion of the frame. Typically, the impeller isdisposed in close proximity to the blood inlet opening throughoutoperation (and the axial back-and-forth motion) of the impeller, withthe distal end of the impeller typically being disposed within 15 mm ofthe blood inlet opening throughout operation of the impeller. For someapplications, having a widened blood inlet opening in close proximity tothe impeller reduces turbulence that is generated as blood flows intothe blood inlet opening. The reduction of turbulence typically increasesblood flow and/or reduces hemolysis that is generated by the impellerrelative to if the frame were to define a non-widened blood inletopening.

Referring to FIG. 19E, for some applications, the combination of theframe, the inner lining, and the portion of tube 24 disposed around theframe is shape set such that a distal portion 332 of cylindrical portion38 of the frame converges from the distal end of the cylindrical portionof the frame and toward the impeller (such as to define a portion of theframe that is narrower than the rest of the cylindrical portion of theframe in the vicinity of the impeller (e.g., in the vicinity of thedistal end of the impeller)). For some applications, having a portion ofthe frame that converges toward the impeller reduces turbulence that isgenerated as blood flows from the blood inlet opening toward theimpeller. The reduction of turbulence typically increases blood flowand/or reduces hemolysis that is generated by the impeller relative toif the frame were not to define the converging portion.

Referring to FIG. 19F, for some applications the combination of theframe, the inner lining, and the portion of tube 24 disposed around theframe is shape set such that the features described, respectively, withreference to FIGS. 19D and 19E are combined. That is to say that a firstdistal portion 330 of the cylindrical portion of the frame is widenedwith respect to the rest of cylindrical portion 38 of the frame, and asecond portion 332 of the cylindrical portion of the frame convergestoward the impeller.

Referring to FIG. 19G, for some applications, tube 24 does not extend tothe distal end of cylindrical portion 38 of frame 34. For some suchapplications, along the portion of the frame along which the tube doesextend, the tube is configured to limit the radial expansion of theframe. Along the distal portion of the cylindrical portion of the frame(over which the tube does not extend), the expansion of the frame is notlimited by tube 24. Therefore, the distal portion of the cylindricalportion of the frame is widened with respect to the portion of thecylindrical portion of the frame that is proximal thereto (over whichtube 24 does extend). For some applications, this results in blood inletopening 108 being wider than it would be if tube 24 were to extend alongthe full length of the cylindrical portion of the frame. As describedwith reference to FIG. 19D, typically, the impeller is disposed in closeproximity to the blood inlet opening throughout operation (and the axialback-and-forth motion) of the impeller, with the distal end of theimpeller typically being disposed within 15 mm of the blood inletopening throughout operation of the impeller. For some applications,having a widened blood inlet opening in close proximity to the impellerreduces turbulence that is generated as blood flows into the blood inletopening. The reduction of turbulence typically increases blood flowand/or reduces hemolysis that is generated by the impeller relative toif the frame were to define a non-widened blood inlet opening.

Referring to FIG. 19H, for some applications, in order to facilitatecoupling of inner lining 39 to frame 34, an outer covering material iscoupled (e.g., using adhesive, vacuum and/or a thermoforming procedure)to the inner lining from outside frame 34 at certain discrete couplingregions 326 along the length of the frame. (It is noted that in FIG. 19,tube 24 and frame 34 are shown in the absence of other components of theventricular assist device (such as the impeller and the axial shaft),for illustrative purposes.) For some applications, at at least one ofthese coupling regions, tube 24 comprises the outer covering material,as shown in the proximal-most coupling region, to the right of FIG. 19G.Alternatively or additionally, an additional outer covering material 328is placed around frame 34 at one or more of the coupling regions. Forexample, the additional coupling material may be made from similarmaterials to those used for inner lining 39 and/or tube 24. For someapplications, at the coupling regions, frame 34 has a lower density ofstruts relative to the density of struts of the frame (i.e., the ratioof the surface area occupied by the struts to the areas of open spacesbetween the struts) at other locations along the length of the frame.For example, as shown in FIG. 19G, along cylindrical portion 38 of theframe, at the coupling regions that frame has straight axial struts 329,whereas at other regions within the cylindrical portion of the frame,the frame defines zigzag struts, and there is a ratio of two zigzagstruts to each straight strut. Typically, the reduced density of strutsat the coupling regions allows the outer covering material to bedirectly coupled to the inner lining over a greater surface area, thanif the frame did not have the reduced strut density at the couplingregion.

Reference is now made to FIGS. 20A, 20B, and 20C, which are schematicillustrations of ventricular assist device 20 that includes aninflatable portion 331 (e.g., a balloon), the inflatable portion beingin respective states of inflation in each of FIGS. 20A, 20B and 20C, inaccordance with some applications of the present invention. For someapplications (as shown), inflatable portion 331 is inflated in agenerally similar manner to that described hereinabove with reference toinflatable portion 153 shown in FIG. 13D. Namely, the inflatable portionis inflated by the purging fluid entering the interior of the inflatableportion, via opening 155. For some applications, by controlling thepressure at which the purging fluid is pumped into ventricular assistdevice 20, the inflation of the inflatable portion is controlled.Alternatively or additionally, an inflation lumen for inflating theinflatable portion is configured to pass through outer tube 142, and tothen pass along the outer surface of tube 24, and to the inflatableportion of the distal-tip portion.

For some applications, the inflatable portion is configured to be inrespective states of inflation during respective phases of thedeployment of ventricular assist device. For some applications,distal-tip portion 120 has a radially-converging shape (as shown inFIGS. 20A-C) and is configured to act as a dilator, during insertion ofventricular assist device via a puncture in the subject's body, asdescribed hereinabove. In this manner, the delivery catheter 143 andcomponents of the ventricular assist device that are disposed within thedelivery catheter can be inserted into the puncture without requiringpre-dilation of the puncture, and without requiring a separateintroducer device, for facilitating insertion of the delivery catheterthrough the puncture. Typically, during the insertion of the distal-tipportion through the puncture in the subject's body, inflatable portion331 is maintained in a deflated state, as shown in FIG. 20A.

For some applications, subsequent to the distal-tip portion beinginserted via the puncture in the subject's body, the distal-tip portionis used to guide the delivery catheter along curved anatomy (e.g., theaortic arch). For some applications, during this stage of the procedure,the inflatable portion is partially inflated, such as to prevent thedistal-tip portion from causing trauma to the patient's vasculature. Theinflatable portion is shown in the partially inflated state in FIG. 20B.

For some applications, upon ventricular assist device 20 being deployedsuch that the distal-tip portion is within the subject's left ventricle,inflatable portion 331 is more fully inflated than in the state of theinflatable portion shown in FIG. 20B (e.g., fully inflated). Typically,when the inflatable portion is more fully inflated, the inflatableportion separates one or more blood inlet openings 108 from innerstructures of the left ventricle in three dimensions. In this manner,the inflatable portion separates one or more blood inlet openings 108from the interventricular septum, chordae tendineae, papillary muscles,and/or the apex of the left ventricle. For some applications, theinflatable portion is shaped such as to direct blood flow from the leftventricle into the one or more blood inlet openings.

Typically, a hemostasis valve (e.g., duckbill valve 390) is disposedwithin lumen 122 of distal-tip portion 120. For some applications, thehemostasis valve prevents blood from flowing into lumen 122, and/or intolumen 132. Typically, the hemostasis valve, by preventing purging fluidfrom flowing out of the distal end of lumen 122, causes the purgingfluid to flow toward the interface between axial shaft 92 and distalbearing 118, as described hereinabove.

Reference is now made to FIG. 21, which is a schematic illustration ofventricular assist device 20 being placed inside a subject's leftventricle 22 (a transverse cross-sectional view of the left ventriclebeing illustrated), in accordance with some applications of the presentinvention. (FIG. 21 shows aortic valve 26 overlaid on the transversecross-section of the left ventricle even though the aortic valve lies ina different plane from the plane of the main cross-sectional view, forillustrative purposes.) Reference is also made to FIGS. 22A-D, which areschematic illustrations of distal-tip element 107 of the ventricularassist device that is at least partially curved such as to define acurvature that is similar to that of a question mark, in accordance withsome applications of the present invention, and to FIGS. 23A and 23B,which are schematic illustrations of the ventricular assist device ofFIGS. 22C-D disposed inside a subject's left ventricle, in accordancewith some applications of the present invention.

For some applications, the ventricular assist device is guided by theguidewire over which it is inserted toward apex 342 of the leftventricle. The walls of the left ventricle may be thought of as beingmade up of the septal wall 338 (which separates the left ventricle fromthe right ventricle 340), the posterior wall 336 (from which thepapillary muscles 341 protrude, and above which the mitral valveapparatus is disposed), and the free wall 334, each of these three wallsoccupying approximately one third of the circumference of the leftventricle (as illustrated by the dashed lines, which trisect the leftventricle in FIG. 21). Typically, it is undesirable for the distal-tipelement (or any other portions of the ventricular assist device) to comeinto contact with the septal wall, since there is a risk that this cangive rise to arrythmias. Further typically, it is desirable to maintaina distance between the distal-tip element (and any other portions of theventricular assist device) from the posterior wall, in order not tointerfere with the mitral valve apparatus, and in order to prevent themitral valve apparatus from interfering with the functioning of theventricular assist device. Therefore, the ventricular assist device istypically guided toward the apex, in such a manner that, if and when thedistal-tip element contacts the inner wall of the left ventricle, itcontacts free wall 334, as shown in FIGS. 21 and 23A-B.

Typically, the ventricular assist device is introduced into thesubject's ventricle over a guidewire, as described hereinabove.Distal-tip portion 120 defines guidewire lumen 122, such that thedistal-tip portion is held in a straightened configuration during theintroduction of the ventricular assist device into the subject'sventricle. For some applications, upon the guidewire being removed,distal-tip portion is configured to assume its curved shape. It is notedthat FIGS. 22A-D illustrate the shape of distal-tip portion 120 as it isinitially formed. Typically, as a result of having the guidewireinserted through guidewire lumen 122 (thereby temporarily straighteningthe distal-tip portion), upon being deployed within the subject's leftventricle, the curvature of the distal-tip portion is less than thatshown in at least some of FIGS. 22A-D. For example, FIGS. 22C-D showthat the curvature of the distal-tip portion is such that the curvedportion of the distal-tip portion forms a complete loop. However, thedistal-tip portion of FIGS. 22C-D is shown in FIG. 23A within thesubject's left ventricle and it does not form a complete loop.

As described hereinabove, distal-tip portion 120 typically forms aportion of distal-tip element 107 which also includes axial-shaftreceiving tube 126. Typically, distal-tip element 107 is configured suchthat in its non-constrained configuration (i.e., in the absence of anyforces acting upon the distal-tip portion), the distal-tip element is atleast partially curved. For some applications, within a given plane,distal-tip element 107 has a proximal, straight portion 346 (at least aportion of which typically comprises axial-shaft-receiving tube 126).The proximal straight portion of distal-tip element 107 defines alongitudinal axis 348. The curved portion of distal-tip element 107curves away from longitudinal axis 348 in a first direction, and thenpasses through an inflection point and curves in the opposite directionwith respect to longitudinal axis 348. For example, as shown in FIGS.22A-B, within the plane of the page, the distal-tip element first curvesto the top of the page, then curves to the bottom of the page, and asshown in FIGS. 22C-D, within the plane of the page, the distal-tipelement first curves to the bottom of the page, then curves to the topof the page. Typically, when shaped as shown in FIGS. 22A-D, thedistal-tip element defines an overall curvature that is similar to thatof a question mark or a tennis-racket, the distal-tip element defining abulge 351 on one side of the longitudinal axis of the straight proximalstraight portion of the distal-tip element. For some applications, thebulge is generally shaped as a semi-ellipse. (It is noted that in thiscontext the term “semi-ellipse” includes a semi-circle. It is furthernoted that is some cases, the tip does not define a precisesemi-ellipse, but rather a bulged shape that is substantially similar toa semi-ellipse.)

As shown in FIGS. 22A-B, for some applications, after passing throughthe inflection point the distal-tip element continues to curve such thatthe distal-tip element crosses back over longitudinal axis 348. FIG. 22Ashows an example in which the end of the distal-tip element does notcross back over the longitudinal axis yet again, and there is a largergap between the distal end of the distal-tip element and the proximalend of the curved portion. FIG. 22B shows an example in which the enddistal-tip element does cross back over the longitudinal axis yet again,and there is a smaller gap between the distal end of the distal-tipelement and the proximal end of the curved portion. As shown in FIGS.22C-D (which are, respectively, cross-sectional and isometric views ofthe same shaped distal-tip element), for some applications, afterpassing through the inflection point the tip does not curve such thatthe distal-tip element crosses back over longitudinal axis 348. Rather,all of the curvature of the curved portion of the distal-tip elementoccurs on one side of longitudinal axis 348.

Referring to FIG. 22A and 22C, typically, a hemostasis valve (e.g.,duckbill valve 390) is disposed within a distal section of distal-tipportion 120, and is configured to prevent blood flow into lumen 122. Forsome applications, the duckbill valve 390 is as described in furtherdetail hereinbelow with reference to FIGS. 28A-C. For example, FIG. 22Ashows an example in which the duckbill valve of FIGS. 28A-C is used.Alternatively, a different duckbill valve is used, e.g., as shown inFIG. 22C. Typically, the duckbill valve has a maximum width of less than3 mm, e.g., less than 2 mm. Typically, the entire duckbill valve isdisposed within a distal section of the distal-tip portion that isdisposed within the distal-most 10 mm, e.g., the distal most 5 mm of thedistal-tip portion. For some applications, the duckbill valve isproximally facing (i.e., such that the wide inlet of the valve faces thedistal end of distal-tip portion and such that the narrow tip of thevalve faces away from the distal end of distal-tip portion 120), asdescribed in further detail hereinbelow with reference to FIGS. 28A-E.For some applications, a guidewire guide 392 is disposed withindistal-tip portion 120 at a location that is proximal to the duckbillvalve (e.g., as shown in FIG. 22A). As shown in FIGS. 22A-D, typically,the distal section of the distal portion is widened in order toaccommodate the duckbill valve and/or the guidewire guide. For someapplications, by virtue of the distal portion being widened, the distaltip of the distal-tip portion (via which a guidewire is inserted intothe distal-tip portion) does not have a sharp edge. Rather the edge hasa width of more than 1 mm. Typically, the lack of a sharp edge at thedistal tip of the distal-tip portion helps to prevent the distal tip ofthe distal-tip portion from causing trauma to structure within the leftventricle.

Typically, upon being deployed within the subject's left ventricle, thecurvature of the curved portion of distal-tip element 107 is configuredto provide an atraumatic tip to ventricular assist device 20. Furthertypically, the distal-tip element is configured to space the inletopenings 108 of the ventricular assist device from walls of the leftventricle.

Referring now to FIGS. 23A and 23B, it is first noted that these figuresshow a cross-sectional view of the left ventricle 22 in which septalwall 338 is disposed on the left of the page and free wall 334 isdisposed on the right of the page. In this view, the left atrium 359,and left atrial appendage 358 are visible above the left ventricle, andright ventricle 340 is visible to the left of the left ventricle. Forsome applications, distal-tip element 107 is configured to separate theblood inlet opening from a posterior wall of the subject's leftventricle when the distal-tip element is placed against the apex of thesubject's left ventricle. Typically, the distal-tip element isconfigured to separate the blood inlet opening from a septal wall of thesubject's left ventricle as the distal-tip element contacts the apex ofthe subject's left ventricle.

Typically, distal-tip element 107 is inserted into the left ventricle,such that bulge 351 bulges toward the septal wall 338. When disposed inthis configuration, in response to distal-tip element 107 being pushedagainst the apex (e.g., due to a physician advancing the device or inresponse to movement of the left ventricle), the blood inlet openingtypically gets pushed in the direction of free wall 334 and away fromthe septal wall 338 (in the direction of the arrows shown in FIG. 23B.Typically, this is due to proximal straight portion 346 pivoting aboutthe curved portion of the question mark shape, as shown. By contrast,other shapes of tips, if disposed in a similar orientation may result inthe blood inlet opening being pushed toward the septal wall. Forexample, if the distal-tip element were to have a pigtail tip (in whichthe tip curves in a single direction of curvature) that is oriented suchthat the pigtail curve is on the free wall side of the longitudinal axisof the straight portion of the distal-tip element, then pushing the tipdistally would typically cause the blood inlet openings toward theseptal wall due to the loop of the pigtail curve tightening.

Reference is now made to FIGS. 24A, 24B, 24C, which are schematicillustrations of distal-tip element 107, the distal-tip element beingconfigured to center itself with respect to aortic valve 26, inaccordance with some applications of the present invention. As shown inFIG. 24A, for some applications, the curved distal portion is shapedthat after curving in the first direction the curved distal portiondefines an elongated straight portion 353, before curving in the seconddirection. As shown in FIG. 24B, the distal-tip element is configuredsuch that upon being released within the subject's aorta, the distal-tipelement centers itself with respect to aortic valve 26. Thus, thedistal-tip portion may be used to guide ventricular assist devicethrough the aortic valve in an atraumatic manner. This may be desirable,for example, in instances in which the ventricular assist device ismistakenly retracted through the aortic valve from the left ventricle,after the distal-tip element has been released within the leftventricle. Referring to FIG. 24C, an alternative or additional manner inwhich to configure the distal-tip element to provide the above-describedfunctionality is for the radius of bulge 351 of the distal-tip elementto be sufficiently large such as to center the distal-tip element withrespect to the aortic valve. For example, the radius of the bulge of thedistal-tip element may be greater than 15 mm (e.g., greater than 17 mm).

With reference to all of FIGS. 21-24C it is noted that the scope of thepresent invention includes using a question-mark or tennis-racket shapeddistal-tip element in combination with any ventricular assist device,and even in the absence of other features and/or portions of distal-tipelement 107 (such as, axial-shaft-receiving tube 126).

Reference is now made to FIG. 25A, which is a schematic illustration ofventricular assist device 20, tube 24 of the device being configured tobecome curved when blood is pumped through the tube, in accordance withsome applications of the present invention. Reference is also made toFIG. 25B, which is a schematic illustration of tube 24 of FIG. 25A, inthe absence of other components of the ventricular assist device, inaccordance with some applications of the present invention. Reference isadditionally made to FIG. 25C, which is a schematic illustration ofventricular assist device 20 of FIGS. 25A-B disposed inside a subject'saorta 30 and left ventricle 22, in accordance with some applications ofthe present invention. It is noted that the view of the aorta and theleft ventricle as shown in FIG. 25C is different to that shown, forexample, in FIG. 1B. FIG. 1B and similar figures are schematicillustrations, provided for illustrative purposes and do not necessarilyprecisely depict the scale and orientation of the ventricular assistwith respect to the anatomy. It is further noted that the view of theaorta and the left ventricle as shown in FIG. 25C is different to thatshown, for example, in FIGS. 23A and 23B. FIG. 25C shows across-sectional view of the left ventricle in which the posterior wall336 is disposed on the left of the page and the free wall 334 isdisposed on the right of the page.

As described hereinabove, for some applications, along a proximalportion of tube 24, frame 34 is not disposed within the tube, and thetube is therefore not supported in an open state by frame 34. Tube 24 istypically made of a blood-impermeable, collapsible material. Forexample, tube 24 may include polyurethane, polyester, and/or silicone.Alternatively or additionally, the tube is made of polyethyleneterephthalate (PET) and/or polyether block amide (PEBAX®). Typically,the proximal portion of the tube is configured to be placed such that itis at least partially disposed within the subject's ascending aorta. Forsome applications, the proximal portion of the tube traverses thesubject's aortic valve, passing from the subject's left ventricle intothe subject's ascending aorta, as shown in FIG. 1B. As describedhereinabove, the tube typically defines one or more blood inlet openings108 at the distal end of the tube, via which blood flows into the tubefrom the left ventricle, during operation of the impeller. For someapplications, the proximal portion of the tube defines one or more bloodoutlet openings 109, via which blood flows from the tube into theascending aorta, during operation of the impeller. During operation ofthe impeller, the pressure of the blood flow through the tube typicallymaintains the proximal portion of the tube in an open state.

For some applications, tube 24 is pre-shaped such that, during operationof the impeller, when the pressure of the blood flow through the tubemaintains the proximal portion of the tube in an open state, the tube iscurved. Typically, the curvature is such that when the proximal end ofthe tube is disposed within the aorta, at least a portion of the tube isdisposed within the left ventricle and curving away from the posteriorwall of the left ventricle, toward the apex of the left ventricle and/ortoward the free wall. Further typically, the curvature is such that whenthe proximal end of the tube is disposed within the aorta, at least aportion of the tube is disposed within the left ventricle and curvingaway from the septal wall of the left ventricle, toward the apex of theleft ventricle and/or toward the free wall. For some applications, thecurvature of the tube is such that a separation is maintained betweenblood inlet openings 108 and posterior wall 336 of the left ventricle,mitral valve leaflets 402 and/or subvalvular components of the mitralvalve (such as chordae tendineae 404 and/or papillary muscles 341), asshown in FIG. 25C.

Typically, tube 24 is pre-shaped using blow molding in a curved mold, orusing a shaping mold after a blow-molding process or a dipping process.Typically, the distal portion of the tube, within which frame 34,impeller 50 and axial shaft 92 are disposed, is maintained in a straightand open configuration by frame 34. The portion of the tube, which isproximal to frame 34 and which is disposed within the left ventricle, istypically shaped to define the above-described curvature. For someapplications, the curvature is such that an angle gamma between thelongitudinal axis of the tube at the proximal end of the tube, and thelongitudinal axis of the tube at the distal end of the tube is greaterthan 90 degrees (e.g., greater than 120 degrees, or greater than 140degrees), and/or less than 180 degrees (e.g., less than 160 degrees, orless than 150 degrees), e.g., 90-180 degrees, 90-160 degrees, 120-160degrees, or 140-150 degrees. For some applications, the curvature of thetube is such that the surface of the tube that is at the inside of thecurve defines a radius of curvature R that is greater than 10 mm, e.g.greater than 20 mm, and/or less than 200 mm (e.g., 100 mm), e.g., 10-200mm, or 20-100 mm. (A dashed circle with a dashed line across itsdiameter is shown in FIG. 25B, in order to indicate how radius ofcurvature R is measured.)

It is noted that tube 24, as described with reference to FIGS. 25A-C isconfigured such that (a) in the absence of blood flowing through thetube, the tube typically collapses in response to pressure outside thetube exceeding pressure inside the tube, and (b) when blood flowsthrough the tube at a sufficient rate that pressure within the tubeexceeds pressure outside the tube, then the tube assumes its pre-shaped,curved configuration. It is further noted that when tube 24 assumes itscurved configuration, the tube typically causes the portion of drivecable 130 that is disposed within the curved portion of the tube to alsobecome curved, as shown in FIGS. 25A and 25C. That is to say that it isthe pre-shaping of the tube itself that typically causes the tube andthe drive cable to curve, rather than the drive cable (or a differentelement disposed inside the tube) that causes the tube to curve.Alternatively, outer tube 140 and/or 142 (which is disposed around thedrive cable) is shaped to define the curve, and the outer tube causesthe drive cable and tube 24 to assume the curved shapes. For someapplications, both outer tube 140 and/or 142 and tube 24 are shaped todefine curved shapes.

It is noted that tube 24 as shown in FIGS. 25A-C is generally configuredas described hereinabove with reference to FIG. 2A (i.e., with a conicaldistal portion 46, and with a plurality of blood inlet openings 108).However, the scope of the present invention includes combining thecurved configuration of the tube, as described with reference to FIGS.25A-C, with other general configurations of the tube (e.g., as describedhereinabove).

Reference is now made to FIGS. 25D-E, which are schematic illustrationsof ventricular assist device 20, tube 24 of the device being configuredto become curved when blood is pumped through the tube, in accordancewith some applications of the present invention. In FIGS. 25D and 25E,tube 24 is shown in the absence of other components of the ventricularassist device (such as impeller 50, frame 34, etc.), for illustrativepurposes. FIG. 25E is a schematic illustration of ventricular assistdevice 20 of FIG. 25D disposed inside a subject's aorta 30 and leftventricle 22, in accordance with some applications of the presentinvention. The view of the left ventricle shown in FIG. 25E is similarto that shown in FIG. 25C. For some applications, inlet openings 108and/or outlet openings 109 are disposed in a non-axisymmetricconfiguration around tube 24. Typically, tube 24 defines the inletopenings and/or the outlet openings at locations that are such as tocause tube 24 to become curved and/or such as to maintain the curvatureof tube 24 as described with reference to FIGS. 25A-C. For example, asshown, the blood inlet holes may be disposed on the side of tube 24 thatis at the inside of the curve of the tube (or on the inside of thedesired curve of the tube). As blood flows into the blood inlet opening,this lowers the pressure in the region above the blood inlet opening,and the distal end of tube 24 is then pulled toward this region (asindicated by arrow 310). Alternatively or additionally, the blood outletopenings 109 may be disposed on the side of tube 24 that is at theinside of the curve of the tube (or on the inside of the desired curveof the tube). As blood exits the blood outlet openings the blood impactsthe wall of the aorta, which causes the proximal end of tube 24 to bepushed in the opposite direction, in the direction of arrow 312.

As described with reference to FIGS. 25A-C, typically, the curvature ofthe tube is such that a separation is maintained between blood inletopenings 108 and posterior wall 336 of the left ventricle, mitral valveleaflets 402 and/or subvalvular components of the mitral valve (such aschordae tendineae 404 and/or papillary muscles 341), as shown in FIG.25E. Typically, the curvature is such that when the proximal end of thetube is disposed within the aorta, at least a portion of the tube isdisposed within the left ventricle and curving away from the posteriorwall of the left ventricle, toward the apex of the left ventricle and/ortoward the free wall. Further typically, the curvature is such that whenthe proximal end of the tube is disposed within the aorta, at least aportion of the tube is disposed within the left ventricle and curvingaway from the septal wall of the left ventricle, toward the apex of theleft ventricle and/or toward the free wall.

Reference is now made to FIG. 25F, which is a schematic illustration ofventricular assist device 20, the ventricular assist device including acurved element 410 that is configured to provide tube 24 with apredefined curvature, in accordance with some applications of thepresent invention. For some applications, as an alternative or inaddition to tube 24 itself being shaped to define a curve (e.g., asdescribed with reference to FIGS. 24A-E), the ventricular assist deviceincludes curved element 410. Typically, the curved element is made of ashape-memory material, e.g., a shape-memory alloy, such as nitinol. Forsome applications, the curved element is formed from a nitinol tube thatis cut to define holes or slits, such that the tube is able to bepre-shaped in the desired curved shape. For example, the nitinol elementmay be what is known in the art as a nitinol “hypotube” (i.e., a nitinoltube with micro-engineered features along its length). Typically, curvedelement 410 is disposed around drive cable 130 along a longitudinalsection of the drive cable that is proximal to (e.g., immediatelyproximal to) proximal radial bearing 116. For some applications, alongthis longitudinal section of the drive cable, the curved element is usedin place of outer tube 142.

For some applications, the curved element is shape set to have acurvature that is generally similar to that described with respect totube 24, with reference to FIGS. 25A-E. For some applications, thecurvature is such that angle omega between the longitudinal axis of thecurved element at the proximal end of the curved element, and thelongitudinal axis of the curved element at the distal end of the curvedelement is greater than 90 degrees (e.g., greater than 120 degrees, orgreater than 140 degrees), and/or less than 180 degrees (e.g., less than160 degrees, or less than 150 degrees), e.g., 90-180 degrees, 90-160degrees, 120-160 degrees, or 140-150 degrees. For some applications, thecurvature of the tube is such that the surface of the curved elementthat is at the inside of the curve defines radius of curvature that isgreater than 10 mm, e.g. greater than 20 mm, and/or less than 200 mm(e.g., 100 mm), e.g., 10-200 mm, or 20-100 mm. As described withreference to FIGS. 25A-C, typically, the curvature of the tube is suchthat a separation is maintained between blood inlet openings 108 andposterior wall 336 of the left ventricle, mitral valve leaflets 402and/or subvalvular components of the mitral valve (such as chordaetendineae 404 and/or papillary muscles 341), as shown in FIG. 25C.Typically, the curvature is such that when the proximal end of the tubeis disposed within the aorta, at least a portion of the tube is disposedwithin the left ventricle and curving away from the posterior wall ofthe left ventricle, toward the apex of the left ventricle and/or towardthe free wall. Further typically, the curvature is such that when theproximal end of the tube is disposed within the aorta, at least aportion of the tube is disposed within the left ventricle and curvingaway from the septal wall of the left ventricle, toward the apex of theleft ventricle and/or toward the free wall.

With reference to FIGS. 25A-F, it is noted that for some applicationstube 24 adopts a curved shape by virtue of outer tube 142 becominganchored to the aorta and distal-tip portion 120 becoming anchored tothe inner wall of the left ventricle (e.g., the free wall in thevicinity of the apex), as described hereinabove. It is further notedthat the curvature of the tube shown in FIGS. 23A-B is less than thatshown in FIGS. 25A-F because FIGS. 23A-B show a different view of thedevice. In the view shown in FIGS. 23A-B, the curvature is typicallyless pronounced than in the view shown in FIGS. 25A-F.

Reference is now made to FIGS. 26A, 26B, 26C, 26D, 26E, and 26F, whichare schematic illustrations of distal-tip element 107 of ventricularassist device 20, the distal-tip element being at least partiallycurved, in accordance with respective applications of the presentinvention. (Distal-tip element 107 is shown in the absence of the distalend of frame 34, in FIGS. 26B-F.) Typically, the ventricular assistdevice is introduced into the subject's ventricle over a guidewire, asdescribed hereinabove. Distal-tip portion 120 defines a guidewire lumen122, such that the distal-tip portion is held in a straightenedconfiguration during the introduction of the ventricular assist deviceinto the subject's ventricle. For some applications, upon the guidewirebeing removed distal-tip portion is configured to assume a shape asshown in one of FIGS. 26A-F.

Typically, distal-tip element 107 is configured such that in itsnon-constrained configuration (i.e., in the absence of any forces actingupon the distal-tip portion), the distal-tip element is at leastpartially curved. For some applications, the distal-tip element curvesaround an angle of more than 90 degrees (e.g., more than 120 degrees),and less than 180 degrees (e.g., less than 160 degrees), e.g., 90-180degrees, 120-180 degrees, or 120-160 degrees, e.g., as shown in FIG.26A.

For some applications, the distal-tip element defines a first proximalcurved portion 343, and defines a second distal curved portion 344, asshown in FIG. 26B. For some applications, the first curve defines anangle theta of more than 130 degrees (e.g., more than 140 degrees),and/or less than 160 degrees (e.g., less than 150 degrees), e.g.,130-160 degrees, or 140-150 degrees. For some applications, the secondcurve defines an angle alpha of more than 110 degrees (e.g., more than120 degrees), and/or less than 140 degrees (e.g., less than 130degrees), e.g., 110-140 degrees, or 120-130 degrees. Typically, thestiffness of curved portions 343, 344 of the distal-tip element 107 isless than that of a proximal straight portion 346 of the distal-tipelement, which is disposed proximally to both curved portions. For someapplications, the stiffness of second curved portion 344 is less thanthat of first proximal curved portion 343.

Referring to FIGS. 26C and 26D, for some applications, within a givenplane, distal-tip element has proximal, straight portion 346 thatdefines a longitudinal axis 348, curves away from longitudinal axis 348in a first direction, and then curves in the opposite direction withrespect to longitudinal axis 348. For example, as shown in FIG. 26C,within the plane of the page, the distal-tip element first curves to theleft of the page, then curves to the right of the page, and then curvesagain to the left of the page. Or, as shown in FIG. 26D, within theplane of the page, the distal-tip element first curves to the right ofthe page and then curves to the left of the page. (The example shown inFIG. 26D is generally similar to that shown in FIG. 22A, except that theportion of the tip disposed distally to where the tip intersectslongitudinal axis 348 is shorter in FIG. 26D than in FIG. 22).

It is noted that when shaped as shown in FIG. 26C, distal-tip element107 typically defines a first turning point 347 which is disposed on afirst side of a longitudinal axis 348 of proximal straight portion 346of distal-tip portion 120 (e.g., the left side of the longitudinal axis,as shown in FIG. 26C), and a second turning point 349, which is disposedon the opposite side of longitudinal axis 348 of proximal straightportion 346 of distal-tip portion 120 (e.g., the right side of thelongitudinal axis, as shown in FIG. 26C). For some applications, thedistal-tip portion is thereby shaped to defined two bulges on respectivesides of longitudinal axis 348. Typically, the distal bulge 412 islarger (e.g., wider) than proximal bulge 411, as shown. For someapplications, the bulges are generally shaped as semi-ellipses.Typically, the distal semi-ellipse defines a larger radius than that ofthe proximal semi-ellipse, as shown. (It is noted that in this contextthe term “semi-ellipse” includes a semi-circle. It is further noted thatis some cases, the tip does not define two precise semi-ellipses, butrather bulged shapes that are substantially similar to semi-ellipses.)

Typically, when shaped as shown in FIG. 26D, the distal-tip elementdefines an overall curvature that is similar to that of a question mark,the tip portion defining a bulge 351 on one side of the longitudinalaxis of the straight proximal straight portion of the distal-tipportion. For some applications, the bulge is generally shaped as asemi-ellipse. (It is noted that in this context the term “semi-ellipse”includes a semi-circle. It is further noted that is some cases, the tipdoes not define a precise semi-ellipse, but rather a bulged shape thatis substantially similar to a semi-ellipse.)

Typically, upon being deployed within the subject's left ventricle, thecurvature of portions of distal-tip element 107 is configured to provideatraumaticity to tip portion 120. Further typically, the distal-tipportion is configured to space the inlet openings 108 of the ventricularassist device from walls of the left ventricle.

For some applications, by curving in at least three directions such asto define turning points on respective sides of longitudinal axis 348(e.g., as shown in FIG. 26C) and/or by curving in at least twodirections (e.g., as shown in FIG. 26D), the distal-tip element isconfigured to absorb forces exerted upon the distal-tip portion by wallsof the left ventricle by a greater amount than if the distal-tip elementwere to curve in a single direction.

For some applications, distal-tip element 107 defines a plurality ofcurves each of which defines a different radius of curvature, and/orcurves is a respective direction e.g., as shown in FIGS. 26E and 26F.

As described hereinabove, for some applications, duckbill valve 390 isdisposed within a distal section of distal-tip portion 120. The duckbillvalve is shown and described in further detail hereinbelow withreference to FIGS. 28A-C.

It is noted that for all of the curved distal-tip elements that aredescribed herein (e.g., with reference to FIGS. 21-24C and FIGS. 26A-F),typically, the curvatures of the distal-tip portion are all within asingle plane. With reference to all shapes of distal-tip portions thatare described herein (e.g., with reference to FIGS. 21-24C) the scope ofthe present invention includes using a question-mark or tennis-racketshaped distal-tip portion in combination with any ventricular assistdevice, and even in the absence of other features and/or portions ofdistal-tip element 107 (such as, axial-shaft-receiving tube 126).

Reference is now made to FIGS. 27A, 27B, and 27C, which are schematicillustrations of atraumatic projections 350 that are configured toextend from the distal end of the distal-tip element 107 of ventricularassist device 20, in accordance with respective applications of thepresent invention. (Projection 350 is shown in the absence of distal-tipelement 107, in FIGS. 27A-C.) For some applications, the atraumaticprojection includes a closed ellipse or a closed circle. Typically, theventricular assist device is introduced into the subject's ventricleover a guidewire, as described hereinabove. Along a proximal portion ofatraumatic projection 350, the atraumatic projection defines a guidewirelumen 352. The closed circle or ellipse of the atraumatic projectiontypically defines holes 354 in its sidewalls, and the guidewire passesthrough these holes. During insertion of the ventricular assist deviceinto the subject's ventricle, the circle or ellipse is typicallyelongated axially, by a proximal portion of the circle or the ellipsebeing held within the delivery catheter. Further typically, a distalportion of the axially-elongated circle or ellipse protrude from thedistal tip of the delivery catheter, and acts as an atraumatic tip forthe delivery catheter, as the catheter passes through the subject'svasculature.

Typically, upon being deployed within the subject's left ventricle,projection 350 is configured to provide an atraumatic tip to distal-tipelement 107. Further typically, the projection is configured to spacethe inlet openings 108 of the ventricular assist device from walls ofthe left ventricle.

FIGS. 27A, 27B, and 27C show respective shapes of projection 350, whenthe projection is in a non-radially-constrained configuration.Typically, projection 350 is configured to assume such shapes when theprojection is deployed inside the subject's left ventricle.

Reference is now made to FIG. 28A, which is a schematic illustration ofduckbill valve 390 and guidewire guide 392 disposed at the distal end ofdistal-tip portion 120 of a ventricular assist device, in accordancewith some applications of the present invention. Reference is also madeto FIGS. 28B and 28C, which are schematic illustrations of views of,respectively, a proximal, narrow end 420 of duckbill valve 390 and adistal, wide end 422 of duckbill valve 390, in accordance with someapplications of the present invention. Reference is additionally made toFIGS. 28D and 28E, which are schematic illustration of a proximal end424 of guidewire guide 392, and a distal end 426 of guidewire guide 392,in accordance with some applications of the present invention.

It is noted that although duckbill valve 390 and guidewire guide 392 areshown at the distal end of a given example of distal-tip element 107,the scope of the present invention includes combining duckbill valve 390and guidewire guide 392 with any of the other examples of a distal-tipelement described herein. Moreover, the scope of the present inventionincludes using duckbill valve 390 and guidewire guide 392 within the tipof any percutaneous device and is not limited to using duckbill valve390 and guidewire guide 392 within a ventricular assist device.

As described hereinabove, typically, duckbill valve 390 has a maximumwidth of less than 3 mm, e.g., less than 2 mm. Typically, the entireduckbill valve is disposed within a distal section of the distal-tipportion that is disposed within the distal-most 10 mm, e.g., the distalmost 5 mm of the distal-tip portion. Further typically, as shown, theduckbill valve is proximally facing (i.e., such that the wide inlet ofthe duckbill valve faces the distal end of distal-tip portion and suchthat the narrow tip of the duckbill valve faces away from the distal endof distal-tip portion 120). This is because typically the pressure ofthe fluid that is pumped into distal-tip portion (e.g., as describedhereinabove with reference to FIGS. 13A-C) is greater than the pressureof the blood in the left ventricle. The duckbill valve is proximallyfacing, so as to prevent the fluid from flowing out of the distal end ofthe distal portion, such that the fluid flows back toward distal bearing118, as described hereinabove. Typically, blood does not flow intoguidewire lumen 122, since the pressure inside guidewire lumen 122 isgreater than the pressure of the blood in the left ventricle, outsidethe lumen.

Typically, ventricular assist device is advanced to the left ventriclevia a guidewire (e.g., guidewire 10, shown in FIG. 1B). The guidewire istypically inserted into guidewire lumen 122 of distal-tip portion 120via the distal end of the distal-tip portion. Typically, insertion ofthe guidewire through the distal end of the distal-tip portion isrelatively straightforward, since distal, wide end 422 of duckbill valve390 guides the guidewire through the duckbill valve.

For some applications, when ventricular assist device is disposed insidethe subject's body, it is desirable to insert another guidewire from aproximal end of the ventricular assist device to the distal end of thedistal-tip portion. For example, if a further procedure is going to beperformed with respect to the subject's left ventricle subsequent to theoperation of the left ventricular device, then rather than retractingventricular assist device and having to reinsert a guidewire through apercutaneous puncture, it may be desirable to utilize the existingpercutaneous puncture and to insert the guidewire via guidewire lumen122, before retracting ventricular assist device 20.

Typically, in order to facilitate insertion of a guidewire throughguidewire lumen 122 from a proximal end of the ventricular assistdevice, the ventricular assist device includes guidewire guide 392.Guidewire guide 392 is configured to facilitate insertion of theguidewire through narrow proximal end 420 of duckbill valve 390.Guidewire guide is shaped to define a hole 432 therethrough, whichnarrows in diameter from proximal end 424 of the guidewire guide todistal end 426 of the guidewire guide. The shape of the guidewire guideis configured to guide the tip of the guidewire toward a slit 434 at thenarrow, proximal end of the duckbill valve. For some applications, theduckbill valve is additionally shaped to define a converging guideportion 430 at its proximal end, the converging guide portion convergingtoward slit 434, such that the guide portion is configured to furtherguide the tip of the guidewire toward slit 434.

The scope of the present invention includes using duckbill valve 390 andguidewire guide 392 within a guidewire lumen of any percutaneous deviceand is not limited to using duckbill valve 390 and guidewire guide 392within a ventricular assist device. Typically, duckbill valve 390 andguidewire guide 392 facilitate insertion of a guidewire via theguidewire lumen from a proximal end of the device to a distal end of thedevice.

Reference is now made to FIG. 29, which is a schematic illustration of adelivery catheter that includes a sheath 440 configured to facilitatereinsertion of a guidewire through a percutaneous puncture, inaccordance with some applications of the present invention. Typicallythe sheath comprises a covering (e.g., a polyurethane, polyester,silicone, polyethylene terephthalate (PET), and/or polyether block amide(PEBAX®) covering) that is disposed around at least a portion of thecircumference of delivery catheter 143 along a distal section of thelength of the delivery catheter (e.g., along a length of more than 10mm, and/or less than 100 mm, e.g. 10-100 mm), as shown. As describedwith reference to FIGS. 28A-E, for some applications, when ventricularassist device is disposed inside the subject's body, it is desirable toinsert another guidewire through the existing percutaneous puncture,rather than retracting ventricular assist device and then having toreinsert a guidewire through a percutaneous puncture. For someapplications, ventricular assist device and the delivery catheter areretracted until the proximal end of sheath 440 has been retracted fromthe percutaneous puncture. Subsequently, a guidewire is inserted throughthe existing percutaneous puncture, by being advanced through the sheath440 (i.e. between the covering and the outer surface of deliverycatheter 143). The ventricular assist device and delivery catheter maythen be removed from the percutaneous puncture, leaving the guidewire inplace. For some applications, sheath 440 is disposed around a portion ofouter tube 142 along a distal section of the length of the outer tube,the functionality of the sheath being generally as described above.

The scope of the present invention includes using sheath 440 on any typeof percutaneous catheter, so as to facilitate reinsertion of a guidewirevia an existing percutaneous puncture, and is not limited to being usedwith delivery catheter 143 of ventricular assist device 20.

Reference is now made to FIGS. 30 and 31, which are schematicillustrations of ventricular assist devices 20 that include twoimpellers 50, in accordance with some applications of the presentinvention. As shown in FIG. 30, for some applications, first and secondimpellers are disposed in parallel with each other, each of theimpellers being driven by a respective drive cable 130. Typically, afirst one of the impellers 50 and its corresponding frame 34 aredisposed distally of a second impeller one of the impellers 50 and itscorresponding frame 34, such that the impellers and frames are not inoverlapping configurations with one another when they are disposed inradially constrained configurations within delivery catheter 143. Forsome applications, the proximal impeller pumps blood via a parallel tube24A that runs parallel to tube 24, with fluid flow from parallel tube24A flowing into tube 24 at a location that is configured to bedownstream of the aortic valve 26 (the location of aortic valve 26 beingillustrated schematically in FIG. 30). Thus, typically only tube 24(without parallel tube 24A) passes through the aortic valve.

As shown in FIG. 31, for some applications, first and second impellersare disposed series with each other, each of the impellers being drivenby a single drive cable 130. Typically, a first one of the impellers 50and its corresponding frame 34 are disposed distally of a secondimpeller one of the impellers 50 and its corresponding frame 34, suchthat the impellers and frames are not in overlapping configurations withone another when they are disposed in radially constrainedconfigurations within delivery catheter 143. Further typically, theimpellers pump blood into respective blood inlet openings 108 andinitially one of the impeller pumps blood through tube 24, while thesecond impeller pumps blood through parallel tube 24A of tube 24.Typically, fluid flow from parallel tube 24A flows into tube 24 at alocation that is configured to be downstream of the aortic valve (thelocation of the aortic valve being illustrated schematically in FIG.30). Thus, typically only tube 24 (without parallel tube 24A) passesthrough the aortic valve.

It is noted that, by having one of the impellers pump through paralleltube 24A while the second one of the impellers pumps blood via tube 24,it is not that case that the proximal impeller is pumping blood that hasalready been pumped by the distal impeller. It has been found by theinventors that, if a proximal impeller is used to pump blood that hasalready been pumped by a distal impeller, this can result in inefficientpumping of the blood by the proximal impeller. It is further noted thatdoubling the number of impellers will typically double the amount ofhemolysis that is generated by ventricular assist device 20, ceterisparibus. By contrast, increasing the revolution rate of a singleimpeller and/or increasing the length of an impeller can result is adisproportionate increase in the amount of hemolysis that is generatedby the impeller.

With regards to all aspects of ventricular assist device 20 describedwith reference to FIGS. 1A-31, it is noted that, although Figs. lA and1B show ventricular assist device 20 in the subject's left ventricle,for some applications, device 20 is placed inside the subject's rightventricle, such that the device traverses the subject's pulmonary valve,and techniques described herein are applied, mutatis mutandis. For someapplications, components of device 20 are applicable to different typesof blood pumps. For example, aspects of the present invention may beapplicable to a pump that is used to pump blood from the vena cavaand/or the right atrium into the right ventricle, from the vena cavaand/or the right atrium into the pulmonary artery, and/or from the renalveins into the vena cava. Such aspects may include features of tube 24(e.g., the curvature of the tube), impeller 50, features of pump portion27, drive cable 130, apparatus and methods for measuring blood pressure,etc. Alternatively or additionally, device 20 and/or a portion thereof(e.g., impeller 50, even in the absence of tube 24) is placed inside adifferent portion of the subject's body, in order to assist with thepumping of blood from that portion. For example, device 20 and/or aportion thereof (e.g., impeller 50, even in the absence of tube 24) maybe placed in a blood vessel and may be used to pump blood through theblood vessel. For some applications, device 20 and/or a portion thereof(e.g., impeller 50, even in the absence of tube 24) is configured to beplaced within the subclavian vein or jugular vein, at junctions of thevein with a lymph duct, and is used to increase flow of lymphatic fluidfrom the lymph duct into the vein, mutatis mutandis. Since the scope ofthe present invention includes using the apparatus and methods describedherein in anatomical locations other than the left ventricle and theaorta, the ventricular assist device and/or portions thereof aresometimes referred to herein (in the specification and the claims) as ablood pump.

Some examples of devices that include components of ventricular assistdevice 20, but that are used at different anatomical locations aredescribed hereinbelow with reference to FIGS. 32A-33.

Reference is now made to FIGS. 32A, 32B, 32C, 32D, and 32E, which areschematic illustration of a cardiac assist device 360 that is configuredto assist the functioning of the right heart of a subject, in accordancewith some applications of the present invention. For components ofdevice 360 that are generally similar to components describedhereinabove with reference to ventricular assist device 20, the samereference numerals are used as those used hereinabove. Typically, suchcomponents are generally as described hereinabove, except for thedifferences that are described below.

FIG. 32E shows device 360 in its non-radially-constrained configurationin the absence of the subject's anatomy. As shown, typically, to assistthe functioning of the subject's right heart, impeller 50 and frame 34are disposed at a proximal end of tube 24. Similarly, blood inletopening(s) is disposed at the proximal end of the tube. The impeller isconfigured to pump blood through tube 24 in the distal direction, towardblood outlet openings 109 that are disposed at the distal end of tube24. For some applications, a balloon 362 is disposed at the distal endof the device. Balloon 362 is configured to facilitate introduction ofthe distal end of the device into the pulmonary artery 364, by theballoon migrating to the pulmonary artery with the subject's blood flow.Typically, the blood outlet opening(s) is configured to be disposedwithin the pulmonary artery, such that the impeller pumps blood via tube24, into the pulmonary artery.

As shown in FIG. 32A, for some applications, the blood inlet opening(s)108 is disposed within the subject's right ventricle 366, such that theimpeller pumps blood from the right ventricle, via tube 24, intopulmonary artery 364. Alternatively, the blood inlet opening(s) 108 isdisposed within the subject's right atrium 368, such that the impellerpumps blood from the right atrium, via tube 24, into pulmonary artery364, as shown in FIG. 32B. Further alternatively, the blood inletopening(s) 108 is disposed within the subject's superior vena cava 370,such that the impeller pumps blood from the superior vena cava, via tube24, into pulmonary artery 364, as shown in FIG. 32C. Furtheralternatively, the blood inlet opening(s) 108 is disposed within thesubject's inferior vena cava 372, such that the impeller pumps bloodfrom the inferior vena cava, via tube 24, into pulmonary artery 364, asshown in FIG. 32D.

It is noted that, in the configurations shown in FIGS. 32B-D, thecardiac assist device will lower preload on the right heart (by pumpingblood from the right atrium or the vena cava), but will increaseafterload (by pumping blood into the pulmonary artery). By contrast, inthe configuration shown in FIG. 32A, the cardiac assist deviceeffectively does not increase afterload, since the volume of blood thatis pumped into the pulmonary artery by the impeller, is the same volumeas is pumped out of the right ventricle.

Reference is now made to FIG. 33, which is a schematic illustration of avenous assist device 380, in accordance with some applications of thepresent invention. For components of device 380 that are generallysimilar to components described hereinabove with reference toventricular assist device 20, the same reference numerals are used asthose used hereinabove. Typically, such components are generally asdescribed hereinabove, except for the differences that are describedbelow. For some applications, venous assist device 380 includes impeller50 and frame 34, which are generally as described hereinabove. For someapplications, the venous assist device does not include tube 24, forexample, as shown in FIG. 33.

For some applications, venous assist device 380 is inserted into a veinof a subject in order to assist with the pumping of blood through thevein. For example, the venous assist device may be inserted into a vein382 of a leg of a subject (such as the iliac vein or the femoral vein)suffering from an ischemic leg, and may be used to assist with thepumping of blood through the vein.

For some applications, the scope of the present application includes anyone of the following apparatus and methods combined in combination withany of the other apparatus and methods described herein:

A Method Including:

coupling a rigid tube to a drive cable that includes a plurality ofcoiled wires, by:

-   -   placing ends of the drive cable and the rigid tube at a given        location within a butt-welding overtube,        -   the ends of the drive cable and the rigid tube being visible            when they are disposed at the given location within the            butt-welding overtube via a window defined by the            butt-welding overtube, and        -   the placement of the drive cable within the butt-welding            overtube being such that a helical groove defined by a            portion of the butt-welding overtube is disposed over the            drive cable; and    -   forming welding rings around the butt-welding overtube.

For some applications, forming welding rings around the butt-weldingovertube includes forming welding rings that are spaced from edges ofthe butt-welding overtube, such that the welding rings weld thebutt-welding overtube to the rigid tube and the drive cable without thewelding rings being welded directly onto outer surfaces of the rigidtube and the drive cable. For some applications, forming welding ringsaround the butt-welding overtube includes forming welding rings to adepth that is such that that the butt-welding overtube is welded to therigid tube and the drive cable, without reducing a diameter of a lumendefined by the rigid tube and the drive cable. For some applications,forming welding rings around the butt-welding overtube includes formingat least one welding ring at the given location within the butt-weldingovertube at which the ends of the drive cable and the rigid tube areplaced. For some applications, coupling the drive cable to the rigidtube includes coupling the drive cable to an axial shaft that isconfigured to support an impeller. For some applications, coupling thedrive cable to the rigid tube includes coupling the drive cable to a pinthat is configured to be coupled to a magnet, the magnet beingconfigured to be driven to rotate by a motor. Some examples of suchapplications are described hereinabove with reference to FIGS. 10D-E.

Apparatus Including:

a drive cable including a plurality of coiled wires;

a rigid tube configured to be coupled to the drive cable; and

a butt-welding overtube, the butt-welding overtube configured tofacilitate butt-welding of the drive cable to the rigid tube, thebutt-welding overtube defining:

-   -   a window configured to facilitate placement of ends of the drive        cable and the rigid tube at a given location within the        butt-welding overtube, by providing visibility of the ends of        the drive cable and the rigid tube when they are disposed at the        given location within the butt-welding overtube; and    -   a helical groove within a portion of the butt-welding overtube        that is configured to be disposed over the drive cable, and to        provide flexibility to the portion of the butt-welding overtube        that is configured to be disposed over drive cable.

For some applications, the apparatus includes an impeller, and the rigidtube includes an axial shaft that is configured to support the impeller.For some applications, the apparatus includes a motor and a magnetconfigured to be driven to rotate by the motor, and the rigid tubeincludes a pin that is configured to be coupled to the magnet. Someexamples of such applications are described hereinabove with referenceto FIGS. 10D-E.

A Method Including:

coupling to each other first and second portions of drive cable thatincludes a plurality of coiled wires, by:

-   -   placing ends of the first and second portions of the drive cable        at a given location within a butt-welding overtube,        -   the ends of the first and second portions of the drive cable            being visible when they are disposed at the given location            within the butt-welding overtube via a window defined by the            butt-welding overtube, and        -   the placement of at least one of the portions of the drive            cable within the butt-welding overtube being such that a            helical groove defined by a portion of the butt-welding            overtube is disposed over the at least one of the portions            of the drive cable; and    -   forming welding rings around the butt-welding overtube.

Some examples of such applications are described hereinabove withreference to FIGS. 10D-E.

A Method Including:

coupling a rigid tube to a drive cable that includes a plurality ofcoiled wires, by:

-   -   placing ends of the drive cable and the rigid tube at a given        location within a butt-welding overtube,        -   the ends of the drive cable and the rigid tube being visible            when they are disposed at the given location within the            butt-welding overtube via a window defined by the            butt-welding overtube; and    -   forming welding rings around the butt-welding overtube, the        welding rings being spaced from edges of the butt-welding        overtube, such that the welding rings weld the butt-welding        overtube to the rigid tube and the drive cable without being        welded directly onto outer surfaces of the rigid tube and the        drive cable.

For some applications, forming welding rings around the butt-weldingovertube includes forming welding rings to a depth that is such thatthat the butt-welding overtube is welded to the rigid tube and the drivecable, without reducing a diameter of a lumen defined by the rigid tubeand the drive cable. For some applications, forming welding rings aroundthe butt-welding overtube includes forming at least one welding ring atthe given location within the butt-welding overtube at which the ends ofthe drive cable and the rigid tube are placed. For some applications,placing ends of the drive cable and the rigid tube at the given locationwithin the butt-welding overtube includes placing the drive cable withinthe butt-welding overtube such that a helical groove defined by aportion of the butt-welding overtube is disposed over the drive cable.For some applications, coupling the drive cable to the rigid tubeincludes coupling the drive cable to an axial shaft that is configuredto support an impeller. For some applications, coupling the drive cableto the rigid tube includes coupling the drive cable to a pin that isconfigured to be coupled to a magnet, the magnet being configured to bedriven to rotate by a motor. Some examples of such applications aredescribed hereinabove with reference to FIGS. 10D-E.

Apparatus Including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller;    -   a frame configured to be disposed around the impeller;    -   an axial shaft upon which the impeller is disposed;    -   proximal and distal radial bearings, configured to stabilize the        axial shaft radially during rotation of the impeller;    -   an atraumatic distal-tip portion disposed distally with respect        to the impeller, the atraumatic distal-tip portion including an        inflatable portion; and    -   a purging fluid configured to be pumped toward the distal-tip        portion, such as to (a) purge the distal bearing, and (b)        inflate the inflatable portion of the distal-tip portion.

Some examples of such applications are described hereinabove withreference to FIG. 13D.

Apparatus Including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   a tube that defines at least one blood inlet opening and at        least one blood outlet opening;    -   an impeller configured to pump blood of the subject into the        blood inlet opening, through the tube, and out of the blood        outlet opening;    -   a distal-tip portion disposed distally with respect to the blood        inlet opening, the distal-tip portion defining a        radially-converging shape, and being configured to be placed        within a left ventricle of the subject while impeller pumps the        subject's blood;    -   an inflatable portion disposed around the distal-tip portion,        the inflatable portion being configured to define:        -   a) a deflated state, the distal-tip portion being configured            to function as a dilator, during insertion of the blood pump            via a puncture in skin of the subject, when the inflatable            portion is in its deflated state,        -   b) a first inflation state in which the inflatable portion            is configured to prevent the distal-tip portion from causing            trauma to vasculature of the subject, during advancement of            the distal-tip portion through the subject's vasculature,            and        -   c) a second inflation state, in which the inflatable portion            is more fully inflated than in the first inflation state,            the inflatable portion when in its second inflation state            being configured to separate the one or more blood inlet            openings from inner structures of the subject's left            ventricle in three dimensions, when the distal-tip portion            is disposed within the subject's left ventricle.

Some examples of such applications are described hereinabove withreference to FIGS. 20A-C.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured such that a proximal portion of the tube        traverses an aortic valve of the subject, and a distal portion        of the tube is disposed within a left ventricle of the subject;    -   a frame disposed within the distal portion of the tube, the        frame being configured to hold the distal portion of the tube in        an open state,    -   the frame not being disposed within the proximal portion of the        tube, and the proximal portion of the tube thereby being        configured to collapse inwardly in response to pressure outside        of the proximal portion of the tube exceeding pressure inside        the proximal portion of the tube;    -   a pump disposed within the frame and configured to pump blood        through the tube from the subject's left ventricle to the        subject's aorta, such that during pumping of the blood through        the tube:        -   the proximal portion of the tube is maintained in an open            state, and        -   at least a portion of the tube becomes curved, such that the            tube curves away from a posterior wall of the left            ventricle.

For some applications, the pump is configured to pump blood through thetube from the subject's left ventricle to the subject's aorta, such thatduring pumping of the blood through the tube at least the portion of thetube becomes curved, such that the tube curves away from a septal wallof the left ventricle. Some examples of such applications are describedhereinabove with reference to FIGS. 25A-F.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured such that a proximal portion of the tube        traverse an aortic valve of the subject, and a distal portion of        the tube is disposed within a left ventricle of the subject;    -   a frame disposed within the distal portion of the tube, the        frame being configured to hold the distal portion of the tube in        an open state,    -   the frame not being disposed within the proximal portion of the        tube, and the proximal portion of the tube thereby being        configured to collapse inwardly in response to pressure outside        of the proximal portion of the tube exceeding pressure inside        the proximal portion of the tube;    -   a pump disposed within the frame and configured to pump blood        through the tube from the subject's left ventricle to the        subject's aorta, such that during pumping of the blood through        the tube, the proximal portion of the tube is maintained in an        open state;    -   and    -   a curved element disposed within the tube proximally with        respect to the frame, the curved element being configured to        cause at least a portion of the tube to become curved, such that        the tube curves away from a posterior wall of the left        ventricle.

For some applications, the curved element is configured to cause atleast the portion of the tube to becomes curved, such that the tubecurves away from a septal wall of the left ventricle. Some examples ofsuch applications are described hereinabove with reference to FIGS.25A-F.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a tube configured such that a proximal portion of the tube        traverse an aortic valve of the subject, and a distal portion of        the tube is disposed within a left ventricle of the subject;    -   a frame disposed within at least the distal portion of the tube;    -   a pump disposed within the frame and configured to pump blood        through the tube from the subject's left ventricle to the        subject's aorta, by pumping the blood into the tube via a set of        one or more blood inlet openings that are defined by the tube        and that are disposed within the subject's left ventricle, and        by pumping blood out of the tube via a set of one or more blood        outlet openings that are defined by the tube and that are        disposed within the subject's aorta;    -   wherein at least one of the sets of openings in the tube is        disposed in a non-axi-symmetric configuration with respect to        the tube, such that the pumping of the blood through the at        least one of the sets of openings causes at least a portion of        the tube to become curved, such that the tube curves away from a        posterior wall of the left ventricle.

For some applications, the at least one of the sets of openings in thetube is disposed in the non-axi-symmetric configuration with respect tothe tube, such that the pumping of the blood through the at least one ofthe sets of openings causes at least the portion of the tube to becomecurved, such that the tube curves away from a septal wall of the leftventricle. Some examples of such applications are described hereinabovewith reference to FIGS. 25A-F.

Apparatus Including:

an impeller, including:

-   -   an impeller frame that includes proximal and distal end portions        and at least one helical elongate element that winds from the        proximal end portion to the distal end portion;    -   a material that is coupled to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller; and    -   a coil coiled around the at least one helical elongate element,        the coil being configured to facilitate coupling of the material        to the at least one helical elongate element.

A Method, Including:

manufacturing an impeller by:

-   -   forming a structure having first and second end portions at        proximal and distal ends of the structure, the end portions        being connected to one another by at least one elongate element;    -   coiling a coil around the at least one elongate element;    -   causing the at least one elongate element to radially expand and        form at least one helical elongate element, by axially        compressing the structure; and    -   coupling a material to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller,    -   the coil being configured to facilitate coupling of the material        to the helical elongate elements.

Some examples of such applications are described hereinabove withreference to FIGS. 3A-K.

Apparatus Including:

an impeller, including:

-   -   an impeller frame that includes proximal and distal end portions        and at least one helical elongate element that winds from the        proximal end portion to the distal end portion;    -   a material that is coupled to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller; and    -   a sleeve disposed around the at least one helical elongate        element, the sleeve being configured to facilitate coupling of        the material to the at least one helical elongate element.

A Method, Including:

manufacturing an impeller by:

-   -   forming a structure having first and second end portions at        proximal and distal ends of the structure, the end portions        being connected to one another by at least one elongate element;    -   placing a sleeve around the at least one elongate element;    -   causing the at least one elongate element to radially expand and        form at least one helical elongate element, by axially        compressing the structure; and    -   coupling a material to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller,    -   the sleeve being configured to facilitate coupling of the        material to the helical elongate elements.

Some examples of such applications are described hereinabove withreference to FIGS. 3A-K.

Apparatus Including:

an impeller, including:

-   -   an impeller frame that includes proximal and distal end portions        and at least one helical elongate element that winds from the        proximal end portion to the distal end portion, the helical        elongate element having a rounded cross-section; and    -   a material that is coupled to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller; and    -   the roundness of the helical elongate element being configured        to cause the material to form a layer having a substantially        uniform thickness at an interface of the material with the        helical elongate element.

A Method, Including:

manufacturing an impeller by:

-   -   forming a structure having first and second end portions at        proximal and distal ends of the structure, the end portions        being connected to one another by at least one elongate element,        the elongate element having a rounded cross-section;    -   causing the at least one elongate element to radially expand and        form at least one helical elongate element, by axially        compressing the structure; and    -   coupling a material to the at least one helical elongate        element, such that the at least one helical elongate element        with the material coupled thereto defines a blade of the        impeller,    -   the roundness of the helical elongate element being configured        to cause the material to form a layer having a substantially        uniform thickness at an interface between the material and the        helical elongate element.

Some examples of such applications are described hereinabove withreference to FIGS. 3A-K.

A Method, Including:

manufacturing an impeller by:

-   -   forming a structure having first and second end portions at        proximal and distal ends of the structure, the end portions        being connected to one another by at least one elongate element;    -   causing the at least one elongate element to radially expand and        form at least one helical elongate element, by axially        compressing the structure;    -   looping a first end of a looped elongate element around the        helical elongate element, the looped elongate element having a        predefined length and being substantially non- stretchable;    -   inserting a spring along an axis defined by the first and second        end portions, such that a second end of the looped elongate        element is looped around the spring;    -   coupling a material to the at least one helical elongate element        and the spring, such a film of material is supported between the        helical elongate element and the spring, the film of material        defining a blade of the impeller,    -   the looped elongate element being configured to maintain the        helical elongate element within a given distance from the        spring.

Some examples of such applications are described hereinabove withreference to FIGS. 3A-K.

Apparatus Including:

a left ventricular blood pump including:

-   -   an impeller;    -   a motor configured to drive the impeller to pump blood from a        left ventricle of a subject to an aorta of the subject by        rotating the impeller; and    -   a computer processor configured to measure power consumption by        the motor that is required to rotate the impeller at a given        rotation rate, and to determine left ventricular blood pressure        of the subject at least partially in response thereto.

Some examples of such applications are described hereinabove withreference to FIG. 9.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a blood-pump tube configured such that a proximal portion of the        tube traverses an aortic valve of the subject, and a distal        portion of the tube is disposed within a left ventricle of the        subject, the tube defining at least one blood inlet opening that        is configured to be disposed within the left ventricle and at        least one blood outlet opening that is configured to be disposed        within an aorta of the subject;    -   an impeller configured to pump blood through the tube from the        subject's left ventricle to the subject's aorta, by pumping the        blood into the tube via one or more blood inlet openings that        are defined by the tube and that are disposed within the        subject's left ventricle, and by pumping blood out of the tube        via one or more blood outlet openings that are defined by the        tube and that are disposed within the subject's aorta;    -   a drive cable configured to extend from the impeller to outside        the subject's body;    -   one or more outer tubes within which the drive cable is        configured to rotate;    -   a motor disposed outside the subject's body and configured to        drive the impeller to rotate, via the drive cable; and    -   a stator configured to reduce rotational flow components from        blood flow through the blood-pump tube, prior to the blood        flowing from the at least one outlet opening, the stator        including:        -   a frame that is coupled to the one or more outer tubes,            within the blood-pump tube; and        -   a flexible material that is coupled to the frame, such that            in a non-radially-constrained configuration of the stator,            the stator defines a plurality of curved projections that            extend radially from the one or more outer tubes.

For some applications, the frame is a self-expandable frame. Someexamples of such applications are described hereinabove with referenceto FIGS. 14A-C.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a blood-pump tube configured such that a proximal portion of the        tube traverses an aortic valve of the subject, and a distal        portion of the tube is disposed within a left ventricle of the        subject, the tube defining at least one blood inlet opening that        is configured to be disposed within the left ventricle and at        least one blood outlet opening that is configured to be disposed        within an aorta of the subject;    -   an impeller configured to pump blood through the tube from the        subject's left ventricle to the subject's aorta, by pumping the        blood into the tube via one or more blood inlet openings that        are defined by the tube and that are disposed within the        subject's left ventricle, and by pumping blood out of the tube        via one or more blood outlet openings that are defined by the        tube and that are disposed within the subject's aorta;    -   the blood-pump tube defining a stator that is configured to        reduce rotational flow components from blood flow through the        blood-pump tube, prior to the blood flowing from the at least        one outlet opening.

For some applications, the stator includes one or more curved ribbonsthat curve within the blood-pump tube. For some applications, the statorincludes a plurality of ribbons disposed within the blood-pump tube,such as to separate the blood-pump tube into a plurality ofcompartments. For some applications, the stator includes a portion ofthe blood-pump tube that includes a plurality of helical tubes. For someapplications, the stator includes a portion of the blood-pump tube thatis twisted, such that walls of the tube define folds that are such as toreduce rotational flow components from the blood flow through theblood-pump tube, prior to the blood flowing from the at least one outletopening. Some examples of such applications are described hereinabovewith reference to FIGS. 15A-E.

Apparatus Including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller including proximal and distal bushings;    -   a frame configured to be disposed around the impeller;    -   proximal and distal radial bearings disposed, respectively, at        proximal and distal ends of the frame;    -   an axial shaft configured to pass through the proximal and        distal radial bearings and the proximal and distal bushings of        the impeller,    -   the distal bushing of the impeller being coupled to the axial        shaft, such that the proximal bushing is held in an        axially-fixed position with respect to the axial shaft, and    -   the proximal bushing of the impeller not being coupled to the        axial shaft, such that the proximal bushing is not held in an        axially-fixed position with respect to the axial shaft,    -   the impeller being configured to pump blood in a proximal        direction, and the impeller being configured to shorten axially        by the proximal bushing sliding distally with respect to the        axial shaft, in response to pressure exerted upon the impeller        as a result of pumping of blood by the impeller.

Some examples of such applications are described hereinabove withreference to FIGS. 11A-C.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a blood-pump tube configured such that a proximal portion of the        tube traverses an aortic valve of the subject, and a distal        portion of the tube is disposed within a left ventricle of the        subject, the tube defining at least one blood inlet opening that        is configured to be disposed within the left ventricle, at least        one blood outlet opening that is configured to be disposed        within an aorta of the subject, and a central cylindrical        portion;    -   an impeller configured to pump blood through the tube from the        subject's left ventricle to the subject's aorta, by pumping the        blood into the tube via one or more blood inlet openings that        are defined by the tube and that are disposed within the        subject's left ventricle, and by pumping blood out of the tube        via one or more blood outlet openings that are defined by the        tube and that are disposed within the subject's aorta;    -   a pitot tube disposed within the blood-pump tube, the pitot tube        being configured to facilitate measurement of blood flow through        the blood-pump tube,    -   the blood-pump tube being shaped to define a region within which        the pitot tube is disposed, the region being disposed within the        central, cylindrical portion of the blood-pump tube, and being        narrowed with respect to the central, cylindrical portion of the        blood-pump tube.

Some examples of such applications are described hereinabove withreference to FIGS. 17A-D.

Apparatus Including:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device including:

-   -   a distal impeller disposed within a first tube, the first tube        defining at least one blood inlet opening, via which the distal        impeller is configured to pump blood into the first tube;    -   a proximal impeller disposed proximally with respect to the        distal impeller, the proximal impeller being disposed within a        second tube that is disposed in parallel with the first tube        along at least a portion of the first and second tubes, and the        second tube defining at least one blood inlet opening, via which        the proximal impeller is configured to pump blood into the        second tube;    -   the first and second tubes combining into a single tube at a        location proximal to the proximal impeller, the single tube        being configured to pass through an aortic valve of the subject,        when the distal and proximal impellers are disposed within a        left ventricle of the subject, and the single tube defining at        least one blood outlet opening, via which the distal and        proximal impellers are configured to pump blood into an aorta of        the subject.

Some examples of such applications are described hereinabove withreference to FIGS. 30-31.

Apparatus Including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller including proximal and distal bushings;    -   a frame configured to be disposed around the impeller;    -   proximal and distal radial bearings disposed, respectively, at        proximal and distal ends of the frame;    -   an axial shaft configured to pass through the proximal and        distal radial bearings and the proximal and distal bushings of        the impeller,    -   a first one of the bushings of the impeller being coupled to the        axial shaft, such that the first bushing is held in an        axially-fixed position with respect to the axial shaft, and    -   a second one of the bushings of the impeller not being coupled        to the axial shaft, such that the second bushing is configured        to slide axially with respect to the axial shaft,    -   the second bushing including a protrusion that protrudes from        its inner surface, and the axial shaft defining a slot in its        outer surface,    -   the protrusion from the inner surface of the second bushing        being configured to slide along the slot defined by the outer        surface of the axial shaft, such as to prevent the second        bushing from rotating with respect to the axial shaft as the        second bushing slides axially with respect to the axial shaft.

For some applications, the slot defined by the outer surface of theaxial shaft defines a stopper at its end, the stopper being configuredto prevent the second bushing from sliding beyond the stopper, bypreventing axial motion of the protrusion from the inner surface of thesecond bushing beyond the stopper. Some examples of such applicationsare described hereinabove with reference to FIGS. 6A-E.

The scope of the present invention includes combining any of theapparatus and methods described herein with any of the apparatus andmethods described in one or more of the following applications, all ofwhich are incorporated herein by reference:

US 2019/0209758 to Tuval, which is a continuation of InternationalApplication No. PCT/IB2019/050186 to Tuval (published as WO 19/138350),entitled “Ventricular assist device, filed Jan. 10, 2019, which claimspriority from:

-   -   US Provisional Patent Application 62/615,538 to Sohn, entitled        “Ventricular assist device,” filed Jan. 10, 2018;    -   US Provisional Patent Application 62/665,718 to Sohn, entitled        “Ventricular assist device,” filed May 2, 2018;    -   US Provisional Patent Application 62/681,868 to Tuval, entitled        “Ventricular assist device,” filed Jun. 7, 2018; and    -   US Provisional Patent Application 62/727,605 to Tuval, entitled        “Ventricular assist device,” filed Sep. 6, 2018;

US 2019/0269840 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2017/051273 to Tuval (publishedas WO 18/096531), filed Nov. 21, 2017, entitled “Blood pumps,” whichclaims priority from US Provisional Patent Application 62/425,814 toTuval, filed Nov. 23, 2016;

US 2019/0175806 to Tuval, which is a continuation of InternationalApplication No. PCT/IL2017/051158 to Tuval (published as WO 18/078615),entitled “Ventricular assist device,” filed Oct. 23, 2017, which claimspriority from US 62/412,631 to Tuval filed Oct. 25, 2016, and US62/543,540 to Tuval, filed Aug. 10, 2017;

US 2019/0239998 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2017/051092 to Tuval (publishedas WO 18/061002), filed Sep. 28, 2017, entitled “Blood vessel tube,”which claims priority from US Provisional Patent Application 62/401,403to Tuval, filed Sep. 29, 2016;

US 2018/0169313 to Schwammenthal, which is the US national phase ofInternational Patent Application PCT/IL2016/050525 to Schwammenthal(published as WO 16/185473), filed May 18, 2016, entitled “Blood pump,”which claims priority from US Provisional Patent Application 62/162,881to Schwammenthal, filed May 18, 2015, entitled “Blood pump;”

US 2017/0100527 to Schwammenthal, which is the US national phase ofInternational Patent Application PCT/IL2015/050532 to Schwammenthal(published as WO 15/177793), filed May 19, 2015, entitled “Blood pump,”which claims priority from US Provisional Patent Application 62/000,192to Schwammenthal, filed May 19, 2014, entitled “Blood pump;”

U.S. Pat. No. U.S. 10,039,874 to Schwammenthal, which is the US nationalphase of International Patent Application PCT/IL2014/050289 toSchwammenthal (published as WO 14/141284), filed Mar. 13, 2014, entitled“Renal pump,” which claims priority from (a) US Provisional PatentApplication 61/779,803 to Schwammenthal, filed Mar. 13, 2013, entitled“Renal pump,” and (b) US Provisional Patent Application 61/914,475 toSchwammenthal, filed Dec. 11, 2013, entitled “Renal pump;”

U.S. Pat. No. 9,764,113 to Tuval, issued Sep. 19, 2017, entitled “Curvedcatheter,” which claims priority from US Provisional Patent Application61/914,470 to Tuval, filed Dec. 11, 2013, entitled “Curved catheter;”and

U.S. Pat. No. 9,597,205 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2013/050495 to Tuval (publishedas WO 13/183060), filed Jun. 6, 2013, entitled “Prosthetic renal valve,”which claims priority from US Provisional Patent Application 61/656,244to Tuval, filed Jun. 6, 2012, entitled “Prosthetic renal valve.”

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. Apparatus comprising: a left-ventricular assist device configured toassist left-ventricular functioning of a subject, the left-ventricularassist device comprising: a tube configured to traverse an aortic valveof a subject, such that a proximal end of the tube is disposed within anaorta of the subject and a distal end of the tube is disposed within aleft ventricle of the subject; a frame disposed within at least aportion of the tube, the frame defining a plurality of cells, and theframe being configured such that, in a non-radially-constrainedconfiguration of the frame, the frame comprises a generally cylindricalportion, a width of each of the cells within the cylindrical portion, asmeasured around a circumference of the cylindrical portion, being lessthan 2 mm; an inner lining that lines at least some of the cylindricalportion of the frame; and an impeller disposed inside the frame suchthat, in a non-radially-constrained configuration of the impeller, at alocation at which a span of the impeller is at its maximum, the impelleris disposed within the cylindrical portion of the frame, such that a gapbetween an outer edge of the impeller and the inner lining is less than1 mm, the impeller being configured: to rotate such as to pump bloodfrom the left ventricle to the aorta, and to be stabilized with respectto the frame, such that, during rotation of the impeller, the gapbetween the outer edge of the impeller and the inner lining ismaintained and is substantially constant.
 2. The apparatus according toclaim 1, wherein the impeller is configured to reduce a risk ofhemolysis by being stabilized with respect to the frame, relative to ifthe impeller were not stabilized with respect to the frame.
 3. Theapparatus according to claim 1, wherein the width of each of the cellswithin the cylindrical portion as measured around the circumference ofthe cylindrical portion is between 1.4 mm and 1.6 mm.
 4. The apparatusaccording to claim 1, wherein the width of each of the cells within thecylindrical portion as measured around the circumference of thecylindrical portion is between 1.6 mm and 1.8 mm.
 5. The apparatusaccording to claim 1, wherein the impeller is configured such that thegap between the outer edge of the impeller and the inner lining is lessthan 0.4 mm.
 6. The apparatus according to claim 1, wherein: theleft-ventricular assist device further comprises an axial shaft andproximal and distal radial bearings disposed, respectively, at proximaland distal ends of the frame, the axial shaft passing through theproximal and distal radial bearings; the impeller is coupled to theaxial shaft; and the impeller is stabilized with respect to the frame bythe impeller being held in a radially-fixed position with respect to theaxial shaft and the axial shaft being rigid.
 7. The apparatus accordingto claim 6, wherein the impeller comprises bushings that are disposedaround the axial shaft, and at least one of the bushings is configuredto be slidable with respect to the axial shaft, wherein the impeller isstabilized with respect to the frame by a region along the axial shaftover which the at least one bushing is configured to be slidable withrespect to the axial shaft being coated with a coating, such as tosubstantially prevent the impeller from vibrating by the coatingreducing a gap between the at least one bushing and the axial shaft. 8.The apparatus according to claim 6, wherein the impeller is stabilizedwith respect to the frame by substantially preventing vibration of theframe with respect to the axial shaft by a ratio of a length of thecylindrical portion of the frame to a total length of the frame beingmore than 1:2.
 9. The apparatus according to claim 8, wherein the ratioof the length of the cylindrical portion of the frame to the totallength of the frame is more than 2:3.
 10. Apparatus comprising: aleft-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left-ventricular assist device comprising:a tube configured to traverse an aortic valve of a subject, such that aproximal end of the tube is disposed within an aorta of the subject anda distal end of the tube is disposed within a left ventricle of thesubject; a frame disposed within at least a portion of the tube, theframe defining a plurality of cells, and the frame being configured suchthat, in a non-radially-constrained configuration of the frame, theframe comprises a generally cylindrical portion; proximal and distalradial bearings disposed, respectively, at proximal and distal ends ofthe frame; an axial shaft that passes through the proximal and distalradial bearings; an inner lining that lines at least some of thecylindrical portion of the frame; and an impeller coupled to the axialshaft inside the frame such that, in a non-radially-constrainedconfiguration of the impeller, at a location at which a span of theimpeller is at its maximum, the impeller is disposed within thecylindrical portion of the frame such that a gap between an outer edgeof the impeller and the inner lining is less than 1 mm, the impellercomprising bushings that are disposed around the axial shaft, at leastone of the bushings being configured to be slidable with respect to theaxial shaft, and the impeller being stabilized with respect to the frameby a region along the axial shaft over which the at least one bushing isconfigured to be slidable with respect to the axial shaft being coatedwith a coating, such as to substantially prevent the impeller fromvibrating by the coating reducing a gap between the at least one bushingand the impeller.
 11. The apparatus according to claim 10, wherein theregion along the axial shaft over which the at least one bushing isconfigured to be slidable with respect to the axial shaft is coated witha diamond-like-carbon coating.
 12. The apparatus according to claim 10,wherein the region along the axial shaft over which the at least onebushing is configured to be slidable with respect to the axial shaft iscoated with a polytetrafluoroethylene coating.
 13. The apparatusaccording to claim 10, wherein the region along the axial shaft overwhich the at least one bushing is configured to be slidable with respectto the axial shaft is coated with a polymeric sleeve.
 14. The apparatusaccording to claim 10, wherein the impeller is configured to reduce arisk of hemolysis by being stabilized with respect to the frame,relative to if the impeller were not stabilized with respect to theframe.
 15. Apparatus comprising: a left-ventricular assist deviceconfigured to assist left-ventricular functioning of a subject, theleft-ventricular assist device comprising: a tube configured to traversean aortic valve of a subject, such that a proximal end of the tube isdisposed within an aorta of the subject and a distal end of the tube isdisposed within a left ventricle of the subject; a frame disposed withinat least a portion of the tube, the frame defining a plurality of cells,and the frame being configured such that, in a non-radially-constrainedconfiguration of the frame, the frame comprises a generally cylindricalportion; proximal and distal radial bearings disposed, respectively, atproximal and distal ends of the frame; an axial shaft that passesthrough the proximal and distal radial bearings; an inner lining thatlines at least some of the cylindrical portion of the frame; and animpeller coupled to the axial shaft inside the frame such that, in anon-radially-constrained configuration of the impeller, at a location atwhich a span of the impeller is at its maximum, the impeller is disposedwithin the cylindrical portion of the frame such that a gap between anouter edge of the impeller and the inner lining is less than 1 mm, theimpeller being stabilized with respect to the frame by substantiallypreventing vibration of the frame with respect to the axial shaft by aratio of a length of the cylindrical portion of the frame to a totallength of the frame being more than 1:2.
 16. The apparatus according toclaim 15, wherein the ratio of the length of the cylindrical portion ofthe frame to the total length of the frame is more than 2:3.
 17. Theapparatus according to claim 15, wherein the impeller is configured toreduce a risk of hemolysis by being stabilized with respect to theframe, relative to if the impeller were not stabilized with respect tothe frame.